Note: The code parts in this article were generated by Claude 4.5 Sonnet which I provided with a clear and detailed description of Capability-Centric Architecture.
INTRODUCTION
The Capability-Centric Architecture represents a unified architectural pattern that bridges the gap between embedded and enterprise systems while providing clear guidance for iterative development. When applied within agile and lean development processes, CCA offers software engineers a structured yet flexible approach to building complex systems incrementally. This article explores how development teams can leverage CCA principles throughout each sprint or increment, from initial requirements gathering through deployment and operations.
Agile development emphasizes iterative delivery of working software, continuous feedback, and adaptive planning. Lean principles focus on eliminating waste, amplifying learning, and delivering value quickly. The Capability-Centric Architecture aligns naturally with both methodologies by organizing systems around cohesive units of functionality called capabilities. Each capability represents a complete, value-delivering unit that can be developed, tested, and deployed independently.
The challenge many teams face is how to apply architectural patterns consistently across sprints without creating rigid structures that inhibit agility. CCA addresses this by providing clear boundaries through capability contracts while allowing internal implementation to evolve freely. The three-layer structure of each capability nucleus, consisting of Essence, Realization, and Adaptation layers, gives teams a consistent mental model that works whether building a new feature or refactoring existing code.
Throughout this article, we will examine the specific activities software engineers should conduct during each increment. We will explore requirements engineering practices that identify capabilities and their contracts, domain modeling techniques that capture the essence layer, architecture baseline establishment that defines the overall system structure, stepwise refinement that grows capabilities incrementally, comprehensive testing strategies that leverage the layered structure, refactoring approaches that maintain architectural integrity, and deployment practices that support continuous delivery.
REQUIREMENTS ENGINEERING IN CAPABILITY-CENTRIC SPRINTS
Requirements engineering in a CCA-based agile process differs from traditional approaches by focusing on identifying capabilities and their contracts rather than creating exhaustive functional specifications. Each sprint begins with requirements activities that clarify what value the increment should deliver and how that value maps to capabilities.
The first step in requirements engineering is capability identification. The team examines user stories, business goals, and technical needs to identify cohesive units of functionality. A capability should deliver complete value either to end users or to other capabilities. For example, in an e-commerce system, "Product Catalog Management" is a capability that provides complete functionality for managing product information. It is not merely a database access layer or a user interface component, but rather a complete vertical slice that includes domain logic, infrastructure integration, and external interfaces.
When identifying capabilities, engineers should ask several key questions. Does this capability have a clear, single-sentence purpose? Can we describe what it provides without describing how it works internally? Does it represent a cohesive unit that could potentially be developed and deployed independently? If the answers are yes, then we likely have identified a valid capability.
Once capabilities are identified, the team defines capability contracts. A contract specifies three essential elements. The provision section declares what the capability offers to others. The requirement section declares what the capability needs from others. The protocol section defines interaction patterns, quality attributes, and behavioral constraints.
Here is an example of defining a contract during requirements engineering:
/**
* Contract for Order Processing Capability
* Defines the interface between order processing and other capabilities
*/
public interface OrderProcessingContract {
/**
* PROVISION - What this capability provides to others
*/
public interface Provision {
/**
* Submit a new order for processing
* Returns order confirmation with unique order ID
*/
OrderConfirmation submitOrder(OrderRequest request);
/**
* Query the status of an existing order
*/
OrderStatus getOrderStatus(String orderId);
/**
* Cancel an order if it has not yet shipped
*/
CancellationResult cancelOrder(String orderId);
}
/**
* REQUIREMENT - What this capability needs from others
*/
public interface Requirement {
/**
* Needs inventory checking from Inventory Management
*/
InventoryContract.Provision inventoryService();
/**
* Needs payment processing from Payment Processing
*/
PaymentContract.Provision paymentService();
/**
* Needs customer information from Customer Management
*/
CustomerContract.Provision customerService();
}
/**
* PROTOCOL - How interactions should occur
*/
public interface Protocol {
/**
* Maximum time for order submission response
*/
long getMaxResponseTimeMs();
/**
* Whether this capability supports idempotent operations
*/
boolean isIdempotent();
/**
* Retry policy for failed operations
*/
RetryPolicy getRetryPolicy();
}
}
This contract definition emerges from requirements discussions. The team identifies what operations the Order Processing capability must support, what dependencies it has on other capabilities, and what quality attributes it must satisfy. Notice that the contract says nothing about how orders will be processed internally. That implementation detail comes later during design and development.
The requirements engineering phase produces several key artifacts. The capability map shows all identified capabilities and their relationships. Contract definitions specify the interfaces between capabilities. Quality attribute scenarios describe non-functional requirements in terms of specific, measurable criteria. User story mappings show how user stories map to capabilities, helping ensure that all user needs are addressed.
An important practice during requirements engineering is dependency analysis. The team examines the requirement sections of all capability contracts to identify dependencies between capabilities. This analysis helps detect potential circular dependencies early, before any code is written. If Capability A requires services from Capability B, and Capability B requires services from Capability A, the team must restructure the capabilities to eliminate the cycle.
For example, suppose the Order Processing capability requires inventory information, and the Inventory Management capability wants to track which customers order which products most frequently. This creates a potential cycle if Inventory Management directly requires customer information from Customer Management, which might later need order history. The solution is to introduce a new capability, perhaps called Customer Analytics, that depends on both Customer Management and Order Processing but is required by neither. This restructuring eliminates the cycle while creating a more cohesive architecture.
Requirements engineering in CCA-based sprints also addresses evolution from the start. The team considers how capabilities might need to change over time and defines versioning strategies. Contracts include version numbers following semantic versioning principles. Major version changes indicate breaking changes to the contract. Minor version changes add new features while maintaining backward compatibility. Patch versions fix bugs without changing the interface.
The result of requirements engineering activities is a clear understanding of what capabilities the sprint will develop or enhance, what contracts those capabilities must fulfill, what dependencies exist between capabilities, and what quality attributes must be satisfied. This understanding guides all subsequent development activities.
DOMAIN MODELING IN EACH INCREMENT
Domain modeling in Capability-Centric Architecture focuses on capturing the essence of each capability. The essence layer contains pure domain logic or algorithmic core that defines what the capability does, independent of any infrastructure or technical concerns. During each sprint, engineers engage in domain modeling to understand and represent this essential logic.
Domain modeling begins with collaborative sessions involving developers, domain experts, and stakeholders. These sessions use techniques from Domain-Driven Design such as event storming, domain storytelling, and model exploration. The goal is to build a shared understanding of the domain concepts, their relationships, and the business rules that govern them.
For the Order Processing capability, domain modeling might identify concepts such as Order, OrderLine, OrderStatus, PricingRule, DiscountPolicy, and OrderValidation. The team explores how these concepts relate to each other and what invariants must be maintained. For example, an order total must equal the sum of all order line totals after applying applicable discounts. An order can only be cancelled if its status is not yet "Shipped".
The domain model is captured in code as the essence layer of the capability. This code has no dependencies on databases, message queues, web frameworks, or other infrastructure. It represents pure business logic that can be understood, tested, and evolved independently.
Here is an example of domain modeling code for the essence layer:
/**
* Essence layer for Order Processing Capability
* Contains pure domain logic with no infrastructure dependencies
*/
public class OrderProcessingEssence {
/**
* Validates an order request according to business rules
* This is pure logic with no side effects
*/
public ValidationResult validateOrder(OrderRequest request) {
ValidationResult result = new ValidationResult();
// Business rule: Order must have at least one line item
if (request.getOrderLines().isEmpty()) {
result.addError("Order must contain at least one item");
}
// Business rule: Each line item must have positive quantity
for (OrderLine line : request.getOrderLines()) {
if (line.getQuantity() <= 0) {
result.addError(
"Line item " + line.getProductId() +
" has invalid quantity"
);
}
}
// Business rule: Order total must not exceed maximum allowed
Money total = calculateTotal(request);
if (total.isGreaterThan(Money.of(100000, "USD"))) {
result.addError("Order total exceeds maximum allowed amount");
}
return result;
}
/**
* Calculates the total cost of an order including discounts
* Pure calculation with no external dependencies
*/
public Money calculateTotal(OrderRequest request) {
Money subtotal = Money.zero("USD");
// Sum all line items
for (OrderLine line : request.getOrderLines()) {
Money lineTotal = line.getUnitPrice()
.multiply(line.getQuantity());
subtotal = subtotal.add(lineTotal);
}
// Apply discount policies
Money discount = calculateDiscount(subtotal, request.getCustomerId());
return subtotal.subtract(discount);
}
/**
* Determines applicable discount based on business rules
*/
private Money calculateDiscount(Money subtotal, String customerId) {
// Business rule: Orders over $1000 get 10% discount
if (subtotal.isGreaterThan(Money.of(1000, "USD"))) {
return subtotal.multiply(0.10);
}
return Money.zero("USD");
}
/**
* Determines whether an order can be cancelled based on its status
*/
public boolean canCancelOrder(OrderStatus status) {
// Business rule: Can only cancel orders that haven't shipped
return status == OrderStatus.PENDING ||
status == OrderStatus.CONFIRMED ||
status == OrderStatus.PROCESSING;
}
/**
* Calculates the new status after a state transition
*/
public OrderStatus calculateNextStatus(
OrderStatus currentStatus,
OrderEvent event
) {
// State machine logic for order status transitions
switch (currentStatus) {
case PENDING:
if (event == OrderEvent.PAYMENT_CONFIRMED) {
return OrderStatus.CONFIRMED;
}
if (event == OrderEvent.CANCELLED) {
return OrderStatus.CANCELLED;
}
break;
case CONFIRMED:
if (event == OrderEvent.PROCESSING_STARTED) {
return OrderStatus.PROCESSING;
}
if (event == OrderEvent.CANCELLED) {
return OrderStatus.CANCELLED;
}
break;
case PROCESSING:
if (event == OrderEvent.SHIPPED) {
return OrderStatus.SHIPPED;
}
break;
case SHIPPED:
if (event == OrderEvent.DELIVERED) {
return OrderStatus.DELIVERED;
}
break;
}
// Invalid transition - return current status
return currentStatus;
}
}
This essence layer code captures the core domain logic for order processing. Notice that it has no dependencies on databases, web frameworks, or other infrastructure. The validation logic, calculation logic, and state transition logic are all expressed as pure functions that can be tested in isolation.
Domain modeling is an iterative activity that continues throughout the sprint. As the team implements features and gains deeper understanding, the domain model evolves. New concepts emerge, existing concepts are refined, and business rules are clarified. The essence layer code is continuously updated to reflect this growing understanding.
An important principle in domain modeling for CCA is to keep the essence layer focused on the "what" rather than the "how". The essence defines what it means for an order to be valid, what the total should be, and what status transitions are allowed. It does not specify how orders are stored in a database, how payment processing is invoked, or how customers are notified. Those concerns belong in the realization and adaptation layers.
The result of domain modeling activities is a clear, testable representation of the core business logic for each capability. This essence layer serves as the foundation for all other development activities. It can be tested thoroughly with fast unit tests. It can be understood by domain experts who may not be technical. It can evolve as business rules change without requiring changes to infrastructure code.
ESTABLISHING THE ARCHITECTURE BASELINE
The architecture baseline defines the overall structure of the system and the relationships between capabilities. In agile development, the baseline is established early but evolves as the system grows. Each sprint may add new capabilities, refine existing ones, or adjust relationships based on learning.
Establishing the architecture baseline begins with creating the capability registry. The registry is a central component that tracks all capabilities in the system, their contracts, and their dependencies. It serves several critical functions including preventing circular dependencies, determining initialization order, and managing capability lifecycle.
Here is an example of the capability registry implementation:
/**
* Central registry for all capabilities in the system
* Manages capability registration, dependency resolution, and lifecycle
*/
public class CapabilityRegistry {
private final Map<String, CapabilityDescriptor> capabilities;
private final Map<String, Set<String>> dependencyGraph;
public CapabilityRegistry() {
this.capabilities = new ConcurrentHashMap<>();
this.dependencyGraph = new ConcurrentHashMap<>();
}
/**
* Register a new capability with the system
* Validates that registration does not create circular dependencies
*/
public void registerCapability(CapabilityDescriptor descriptor) {
String capabilityName = descriptor.getName();
// Check if this registration would create a circular dependency
if (wouldCreateCycle(capabilityName, descriptor.getRequiredContracts())) {
throw new CircularDependencyException(
"Registering " + capabilityName +
" would create a circular dependency"
);
}
// Register the capability
capabilities.put(capabilityName, descriptor);
// Update dependency graph
updateDependencyGraph(capabilityName, descriptor);
}
/**
* Check if adding a capability would create a dependency cycle
*/
private boolean wouldCreateCycle(
String capabilityName,
Set<Class<?>> requiredContracts
) {
// Build temporary graph including the new capability
Map<String, Set<String>> tempGraph = new HashMap<>(dependencyGraph);
Set<String> dependencies = new HashSet<>();
for (Class<?> contract : requiredContracts) {
String provider = findProviderForContract(contract);
if (provider != null) {
dependencies.add(provider);
}
}
tempGraph.put(capabilityName, dependencies);
// Check for cycles using depth-first search
return hasCycle(tempGraph);
}
/**
* Detect cycles in dependency graph using DFS
*/
private boolean hasCycle(Map<String, Set<String>> graph) {
Set<String> visited = new HashSet<>();
Set<String> recursionStack = new HashSet<>();
for (String node : graph.keySet()) {
if (hasCycleUtil(node, graph, visited, recursionStack)) {
return true;
}
}
return false;
}
private boolean hasCycleUtil(
String node,
Map<String, Set<String>> graph,
Set<String> visited,
Set<String> recursionStack
) {
if (recursionStack.contains(node)) {
return true; // Cycle detected
}
if (visited.contains(node)) {
return false; // Already processed this node
}
visited.add(node);
recursionStack.add(node);
Set<String> neighbors = graph.get(node);
if (neighbors != null) {
for (String neighbor : neighbors) {
if (hasCycleUtil(neighbor, graph, visited, recursionStack)) {
return true;
}
}
}
recursionStack.remove(node);
return false;
}
/**
* Calculate the initialization order for all capabilities
* Uses topological sort to ensure dependencies are initialized first
*/
public List<String> getInitializationOrder() {
List<String> order = new ArrayList<>();
Set<String> visited = new HashSet<>();
for (String capability : capabilities.keySet()) {
if (!visited.contains(capability)) {
topologicalSort(capability, visited, order);
}
}
return order;
}
private void topologicalSort(
String capability,
Set<String> visited,
List<String> order
) {
visited.add(capability);
Set<String> dependencies = dependencyGraph.get(capability);
if (dependencies != null) {
for (String dependency : dependencies) {
if (!visited.contains(dependency)) {
topologicalSort(dependency, visited, order);
}
}
}
order.add(capability);
}
/**
* Retrieve a capability descriptor by name
*/
public CapabilityDescriptor getCapability(String name) {
return capabilities.get(name);
}
/**
* Find which capability provides a given contract
*/
private String findProviderForContract(Class<?> contract) {
for (CapabilityDescriptor descriptor : capabilities.values()) {
if (descriptor.provides(contract)) {
return descriptor.getName();
}
}
return null;
}
private void updateDependencyGraph(
String capabilityName,
CapabilityDescriptor descriptor
) {
Set<String> dependencies = new HashSet<>();
for (Class<?> required : descriptor.getRequiredContracts()) {
String provider = findProviderForContract(required);
if (provider != null) {
dependencies.add(provider);
}
}
dependencyGraph.put(capabilityName, dependencies);
}
}
The capability registry is established early in the project and used throughout all sprints. As new capabilities are added, they are registered with the registry. The registry validates that no circular dependencies are created and maintains the dependency graph.
Another key component of the architecture baseline is the capability lifecycle manager. This component uses the registry to initialize, start, stop, and shutdown capabilities in the correct order.
/**
* Manages the lifecycle of all capabilities
* Ensures proper initialization and shutdown sequences
*/
public class CapabilityLifecycleManager {
private final CapabilityRegistry registry;
private final Map<String, CapabilityInstance> instances;
public CapabilityLifecycleManager(CapabilityRegistry registry) {
this.registry = registry;
this.instances = new ConcurrentHashMap<>();
}
/**
* Initialize all capabilities in dependency order
*/
public void initializeAll() {
List<String> initOrder = registry.getInitializationOrder();
for (String capabilityName : initOrder) {
initializeCapability(capabilityName);
}
}
/**
* Initialize a single capability
*/
private void initializeCapability(String capabilityName) {
CapabilityDescriptor descriptor = registry.getCapability(capabilityName);
// Create instance
CapabilityInstance instance = createInstance(descriptor);
// Inject dependencies
injectDependencies(instance, descriptor);
// Call initialize lifecycle method
instance.initialize();
// Store instance
instances.put(capabilityName, instance);
}
/**
* Start all capabilities after initialization
*/
public void startAll() {
List<String> startOrder = registry.getInitializationOrder();
for (String capabilityName : startOrder) {
CapabilityInstance instance = instances.get(capabilityName);
instance.start();
}
}
/**
* Stop all capabilities in reverse order
*/
public void stopAll() {
List<String> stopOrder = registry.getInitializationOrder();
Collections.reverse(stopOrder);
for (String capabilityName : stopOrder) {
CapabilityInstance instance = instances.get(capabilityName);
instance.stop();
}
}
/**
* Shutdown all capabilities and release resources
*/
public void shutdownAll() {
List<String> shutdownOrder = registry.getInitializationOrder();
Collections.reverse(shutdownOrder);
for (String capabilityName : shutdownOrder) {
CapabilityInstance instance = instances.get(capabilityName);
instance.shutdown();
instances.remove(capabilityName);
}
}
private CapabilityInstance createInstance(CapabilityDescriptor descriptor) {
// Use reflection or factory to create capability instance
// Implementation depends on specific technology stack
return descriptor.getFactory().createInstance();
}
private void injectDependencies(
CapabilityInstance instance,
CapabilityDescriptor descriptor
) {
for (Class<?> requiredContract : descriptor.getRequiredContracts()) {
String providerName = findProvider(requiredContract);
CapabilityInstance provider = instances.get(providerName);
Object contractImpl = provider.getContractImplementation(requiredContract);
instance.injectDependency(requiredContract, contractImpl);
}
}
private String findProvider(Class<?> contract) {
for (Map.Entry<String, CapabilityDescriptor> entry :
registry.getAllCapabilities().entrySet()) {
if (entry.getValue().provides(contract)) {
return entry.getKey();
}
}
return null;
}
}
The architecture baseline also includes deployment descriptors that specify how capabilities should be deployed. These descriptors are independent of the capability implementation, allowing the same capability to be deployed in different modes.
The result of establishing the architecture baseline is a working system structure that supports adding new capabilities incrementally. The registry prevents architectural violations such as circular dependencies. The lifecycle manager ensures capabilities are initialized and shutdown correctly. Deployment descriptors provide flexibility in how capabilities are deployed. This baseline provides a solid foundation that remains stable even as the system evolves.
STEPWISE REFINEMENT THROUGH SPRINTS
Stepwise refinement is the process of growing capabilities incrementally across multiple sprints. Rather than attempting to build a complete capability in a single sprint, teams implement capabilities in layers, starting with the most critical functionality and adding features progressively.
The first sprint that introduces a new capability typically focuses on establishing the capability structure and implementing the most essential features. The team creates the capability skeleton with its three layers: essence, realization, and adaptation. They implement the core domain logic in the essence layer, basic infrastructure integration in the realization layer, and minimal interfaces in the adaptation layer.
For example, the first sprint for the Order Processing capability might implement only order submission. The essence layer contains validation and total calculation logic. The realization layer integrates with a database to persist orders. The adaptation layer provides a simple REST API for submitting orders. Order cancellation, status queries, and other features are deferred to later sprints.
Here is an example of the initial capability implementation:
/**
* Order Processing Capability - Initial Implementation
* Sprint 1: Basic order submission only
*/
public class OrderProcessingCapability implements CapabilityInstance {
// Essence layer - pure domain logic
private final OrderProcessingEssence essence;
// Realization layer - infrastructure integration
private final DatabaseConnection database;
private final OrderRepository orderRepository;
// Dependencies injected via contracts
private InventoryContract.Provision inventoryService;
private PaymentContract.Provision paymentService;
public OrderProcessingCapability(
DatabaseConnection database,
OrderRepository orderRepository
) {
this.essence = new OrderProcessingEssence();
this.database = database;
this.orderRepository = orderRepository;
}
@Override
public void initialize() {
// Initialize database schema
database.executeScript("create_orders_table.sql");
}
@Override
public void start() {
// Capability is ready to process orders
}
/**
* Submit a new order - Sprint 1 implementation
*/
public OrderConfirmation submitOrder(OrderRequest request) {
// Step 1: Validate using essence layer
ValidationResult validation = essence.validateOrder(request);
if (!validation.isValid()) {
throw new InvalidOrderException(validation.getErrors());
}
// Step 2: Check inventory availability
for (OrderLine line : request.getOrderLines()) {
boolean available = inventoryService.checkAvailability(
line.getProductId(),
line.getQuantity()
);
if (!available) {
throw new InsufficientInventoryException(line.getProductId());
}
}
// Step 3: Calculate total using essence layer
Money total = essence.calculateTotal(request);
// Step 4: Process payment
PaymentResult payment = paymentService.processPayment(
request.getCustomerId(),
total
);
if (!payment.isSuccessful()) {
throw new PaymentFailedException(payment.getErrorMessage());
}
// Step 5: Create and persist order
Order order = new Order();
order.setOrderId(generateOrderId());
order.setCustomerId(request.getCustomerId());
order.setOrderLines(request.getOrderLines());
order.setTotal(total);
order.setStatus(OrderStatus.CONFIRMED);
order.setPaymentId(payment.getPaymentId());
orderRepository.save(order);
// Step 6: Reserve inventory
for (OrderLine line : request.getOrderLines()) {
inventoryService.reserveInventory(
line.getProductId(),
line.getQuantity(),
order.getOrderId()
);
}
// Step 7: Return confirmation
return new OrderConfirmation(
order.getOrderId(),
order.getStatus(),
order.getTotal()
);
}
private String generateOrderId() {
return "ORD-" + System.currentTimeMillis();
}
@Override
public Object getContractImplementation(Class<?> contractType) {
if (contractType == OrderProcessingContract.Provision.class) {
return new OrderProcessingProvisionImpl(this);
}
return null;
}
@Override
public void injectDependency(Class<?> contractType, Object implementation) {
if (contractType == InventoryContract.Provision.class) {
this.inventoryService = (InventoryContract.Provision) implementation;
} else if (contractType == PaymentContract.Provision.class) {
this.paymentService = (PaymentContract.Provision) implementation;
}
}
@Override
public void stop() {
// No cleanup needed yet
}
@Override
public void shutdown() {
database.close();
}
}
In subsequent sprints, the team adds more features to the capability. Sprint 2 might add order status queries. Sprint 3 might add order cancellation. Sprint 4 might add order history and reporting. Each sprint builds on the previous work, refining and extending the capability.
The stepwise refinement process follows several important principles. First, each increment delivers working, tested functionality. The capability is always in a deployable state, even if it does not yet have all planned features. Second, the essence layer is refined continuously as domain understanding deepens. Business rules are clarified, edge cases are handled, and the domain model becomes more sophisticated. Third, the realization layer evolves to support new features and improve performance. Database schemas are migrated, caching is added, and integration patterns are optimized. Fourth, the adaptation layer expands to support new interaction patterns. REST APIs gain new endpoints, message queue consumers are added, and event publishers are implemented.
An important aspect of stepwise refinement is managing technical debt. As capabilities grow, code can become complex and difficult to maintain. The team regularly refactors to keep the code clean and the architecture clear. Refactoring is not a separate phase but an ongoing activity integrated into every sprint.
The result of stepwise refinement is a system that grows organically while maintaining architectural integrity. Capabilities start simple and become more sophisticated over time. The three-layer structure provides clear boundaries that guide where different types of code belong. Contracts remain stable even as implementations evolve, allowing capabilities to change independently.
TESTING STRATEGIES IN CAPABILITY-CENTRIC SPRINTS
Testing in Capability-Centric Architecture leverages the three-layer structure to provide comprehensive coverage with fast, maintainable tests. Each sprint includes testing activities at multiple levels, from unit tests for the essence layer to integration tests for the realization layer to contract tests that verify interface compliance.
The foundation of the testing strategy is essence layer testing. Because the essence contains pure domain logic with no external dependencies, it can be tested with simple, fast unit tests. These tests run in milliseconds and provide immediate feedback to developers.
Here is an example of essence layer testing:
/**
* Unit tests for Order Processing Essence
* Fast, isolated tests with no infrastructure dependencies
*/
public class OrderProcessingEssenceTest {
private OrderProcessingEssence essence;
@Before
public void setUp() {
essence = new OrderProcessingEssence();
}
@Test
public void testValidateOrder_ValidOrder_ReturnsValid() {
// Arrange
OrderRequest request = new OrderRequest();
request.setCustomerId("CUST-123");
request.addOrderLine(new OrderLine("PROD-1", 2, Money.of(50, "USD")));
request.addOrderLine(new OrderLine("PROD-2", 1, Money.of(75, "USD")));
// Act
ValidationResult result = essence.validateOrder(request);
// Assert
assertTrue("Order should be valid", result.isValid());
assertEquals("Should have no errors", 0, result.getErrors().size());
}
@Test
public void testValidateOrder_EmptyOrder_ReturnsInvalid() {
// Arrange
OrderRequest request = new OrderRequest();
request.setCustomerId("CUST-123");
// No order lines added
// Act
ValidationResult result = essence.validateOrder(request);
// Assert
assertFalse("Order should be invalid", result.isValid());
assertTrue(
"Should have error about empty order",
result.getErrors().contains("Order must contain at least one item")
);
}
@Test
public void testCalculateTotal_MultipleItems_CalculatesCorrectly() {
// Arrange
OrderRequest request = new OrderRequest();
request.setCustomerId("CUST-123");
request.addOrderLine(new OrderLine("PROD-1", 2, Money.of(50, "USD")));
request.addOrderLine(new OrderLine("PROD-2", 3, Money.of(30, "USD")));
// Act
Money total = essence.calculateTotal(request);
// Assert
assertEquals(
"Total should be (2*50) + (3*30) = 190",
Money.of(190, "USD"),
total
);
}
@Test
public void testCalculateTotal_LargeOrder_AppliesDiscount() {
// Arrange
OrderRequest request = new OrderRequest();
request.setCustomerId("CUST-123");
request.addOrderLine(new OrderLine("PROD-1", 10, Money.of(150, "USD")));
// Act
Money total = essence.calculateTotal(request);
// Assert - 10% discount on orders over $1000
// Subtotal: 10 * 150 = 1500
// Discount: 1500 * 0.10 = 150
// Total: 1500 - 150 = 1350
assertEquals(
"Total should include 10% discount",
Money.of(1350, "USD"),
total
);
}
@Test
public void testCanCancelOrder_PendingOrder_ReturnsTrue() {
// Act
boolean canCancel = essence.canCancelOrder(OrderStatus.PENDING);
// Assert
assertTrue("Should be able to cancel pending order", canCancel);
}
@Test
public void testCanCancelOrder_ShippedOrder_ReturnsFalse() {
// Act
boolean canCancel = essence.canCancelOrder(OrderStatus.SHIPPED);
// Assert
assertFalse("Should not be able to cancel shipped order", canCancel);
}
@Test
public void testCalculateNextStatus_PendingToConfirmed_TransitionsCorrectly() {
// Act
OrderStatus nextStatus = essence.calculateNextStatus(
OrderStatus.PENDING,
OrderEvent.PAYMENT_CONFIRMED
);
// Assert
assertEquals(
"Status should transition to CONFIRMED",
OrderStatus.CONFIRMED,
nextStatus
);
}
@Test
public void testCalculateNextStatus_InvalidTransition_MaintainsCurrentStatus() {
// Act - try to ship a pending order directly
OrderStatus nextStatus = essence.calculateNextStatus(
OrderStatus.PENDING,
OrderEvent.SHIPPED
);
// Assert
assertEquals(
"Invalid transition should maintain current status",
OrderStatus.PENDING,
nextStatus
);
}
}
These essence layer tests run extremely fast because they have no dependencies on databases, networks, or other slow resources. A typical test suite with hundreds of essence tests completes in seconds, providing rapid feedback during development.
The next level of testing focuses on the realization layer. These integration tests verify that the capability correctly integrates with infrastructure such as databases, message queues, and external services. Integration tests use test doubles or embedded infrastructure to avoid dependencies on production systems.
/**
* Integration tests for Order Processing Realization Layer
* Tests infrastructure integration with test doubles
*/
public class OrderProcessingRealizationTest {
private OrderProcessingCapability capability;
private TestDatabase testDatabase;
private MockInventoryService mockInventory;
private MockPaymentService mockPayment;
@Before
public void setUp() {
// Set up test infrastructure
testDatabase = new TestDatabase();
testDatabase.initialize();
mockInventory = new MockInventoryService();
mockPayment = new MockPaymentService();
// Create capability with test infrastructure
capability = new OrderProcessingCapability(
testDatabase.getConnection(),
new OrderRepository(testDatabase.getConnection())
);
// Inject mock dependencies
capability.injectDependency(
InventoryContract.Provision.class,
mockInventory
);
capability.injectDependency(
PaymentContract.Provision.class,
mockPayment
);
capability.initialize();
capability.start();
}
@After
public void tearDown() {
capability.stop();
capability.shutdown();
testDatabase.cleanup();
}
@Test
public void testSubmitOrder_ValidOrder_PersistsToDatabase() {
// Arrange
mockInventory.setAvailable("PROD-1", 10);
mockPayment.setSuccessful(true);
OrderRequest request = new OrderRequest();
request.setCustomerId("CUST-123");
request.addOrderLine(new OrderLine("PROD-1", 2, Money.of(50, "USD")));
// Act
OrderConfirmation confirmation = capability.submitOrder(request);
// Assert - verify order was persisted
Order savedOrder = testDatabase.findOrderById(confirmation.getOrderId());
assertNotNull("Order should be saved in database", savedOrder);
assertEquals("Customer ID should match", "CUST-123", savedOrder.getCustomerId());
assertEquals("Order total should match", Money.of(100, "USD"), savedOrder.getTotal());
}
@Test
public void testSubmitOrder_SuccessfulPayment_ReservesInventory() {
// Arrange
mockInventory.setAvailable("PROD-1", 10);
mockPayment.setSuccessful(true);
OrderRequest request = new OrderRequest();
request.setCustomerId("CUST-123");
request.addOrderLine(new OrderLine("PROD-1", 2, Money.of(50, "USD")));
// Act
capability.submitOrder(request);
// Assert - verify inventory was reserved
assertTrue(
"Inventory should be reserved",
mockInventory.wasReserved("PROD-1", 2)
);
}
@Test(expected = PaymentFailedException.class)
public void testSubmitOrder_PaymentFails_DoesNotPersistOrder() {
// Arrange
mockInventory.setAvailable("PROD-1", 10);
mockPayment.setSuccessful(false);
OrderRequest request = new OrderRequest();
request.setCustomerId("CUST-123");
request.addOrderLine(new OrderLine("PROD-1", 2, Money.of(50, "USD")));
// Act
try {
capability.submitOrder(request);
} finally {
// Assert - verify no order was persisted
assertEquals(
"No orders should be in database",
0,
testDatabase.countOrders()
);
}
}
}
Integration tests run slower than unit tests because they involve infrastructure, but they are still fast enough to run frequently during development. They verify that the realization layer correctly integrates with databases, message queues, and other infrastructure.
The third level of testing focuses on contracts. Contract tests verify that capabilities fulfill their contract obligations and that consumers use contracts correctly. These tests ensure that the interface between capabilities remains stable and correct.
/**
* Contract tests for Order Processing Capability
* Verifies that the capability fulfills its contract
*/
public class OrderProcessingContractTest {
private OrderProcessingCapability capability;
private OrderProcessingContract.Provision provision;
@Before
public void setUp() {
// Set up capability with test infrastructure
capability = createTestCapability();
provision = (OrderProcessingContract.Provision)
capability.getContractImplementation(
OrderProcessingContract.Provision.class
);
}
@Test
public void testContract_SubmitOrderMethod_Exists() {
// Verify that the provision implements the required method
assertNotNull(
"Provision should implement submitOrder",
provision
);
// Verify method signature through reflection
Method method = findMethod(provision.getClass(), "submitOrder", OrderRequest.class);
assertNotNull("submitOrder method should exist", method);
assertEquals(
"submitOrder should return OrderConfirmation",
OrderConfirmation.class,
method.getReturnType()
);
}
@Test
public void testContract_ResponseTime_MeetsRequirement() {
// Arrange
OrderRequest request = createValidOrderRequest();
// Act - measure response time
long startTime = System.currentTimeMillis();
provision.submitOrder(request);
long endTime = System.currentTimeMillis();
long responseTime = endTime - startTime;
// Assert - verify response time meets contract requirement
long maxResponseTime = 1000; // 1 second max from contract
assertTrue(
"Response time should be under " + maxResponseTime + "ms",
responseTime < maxResponseTime
);
}
@Test
public void testContract_Idempotency_SubmittingSameOrderTwice() {
// Arrange
OrderRequest request = createValidOrderRequest();
request.setIdempotencyKey("UNIQUE-KEY-123");
// Act - submit same order twice
OrderConfirmation first = provision.submitOrder(request);
OrderConfirmation second = provision.submitOrder(request);
// Assert - should return same order ID (idempotent)
assertEquals(
"Idempotent requests should return same order ID",
first.getOrderId(),
second.getOrderId()
);
}
private OrderRequest createValidOrderRequest() {
OrderRequest request = new OrderRequest();
request.setCustomerId("CUST-123");
request.addOrderLine(new OrderLine("PROD-1", 1, Money.of(50, "USD")));
return request;
}
private Method findMethod(Class<?> clazz, String name, Class<?>... paramTypes) {
try {
return clazz.getMethod(name, paramTypes);
} catch (NoSuchMethodException e) {
return null;
}
}
private OrderProcessingCapability createTestCapability() {
// Create capability with test infrastructure
TestDatabase db = new TestDatabase();
db.initialize();
OrderProcessingCapability cap = new OrderProcessingCapability(
db.getConnection(),
new OrderRepository(db.getConnection())
);
cap.injectDependency(
InventoryContract.Provision.class,
new MockInventoryService()
);
cap.injectDependency(
PaymentContract.Provision.class,
new MockPaymentService()
);
cap.initialize();
cap.start();
return cap;
}
}
Contract tests ensure that capabilities fulfill their promises and that the interfaces between capabilities remain stable. They catch breaking changes early and verify that quality attributes specified in contracts are actually met.
The final level of testing is end-to-end testing. These tests exercise the entire system with multiple capabilities working together. They verify that the system delivers value to users and that all capabilities integrate correctly.
The result of this multi-level testing strategy is comprehensive coverage with fast feedback. Essence tests run in milliseconds and catch logic errors immediately. Realization tests run in seconds and verify infrastructure integration. Contract tests ensure interface stability. End-to-end tests validate the complete system. Together, these tests give the team confidence that the system works correctly and that changes have not broken existing functionality.
REFACTORING IN CAPABILITY-CENTRIC ARCHITECTURE
Refactoring is an essential practice in agile development that keeps code clean, maintainable, and aligned with architectural principles. In Capability-Centric Architecture, refactoring activities focus on maintaining the separation between essence, realization, and adaptation layers, ensuring contracts remain stable, and preventing architectural erosion.
Each sprint includes time for refactoring. As features are added and the codebase grows, certain patterns emerge that indicate refactoring opportunities. Code duplication across capabilities suggests extracting a shared capability. Complex essence layer logic suggests breaking down large methods into smaller, more focused functions. Tangled dependencies in the realization layer suggest introducing additional abstraction.
One common refactoring is extracting shared logic into a new capability. Suppose multiple capabilities need to send notifications to users. Initially, each capability might have its own notification code. As this pattern repeats, the team recognizes that notification is itself a capability that should be extracted and shared.
/**
* Notification Capability extracted from duplicated code
* Provides centralized notification services to other capabilities
*/
public class NotificationCapability implements CapabilityInstance {
// Essence layer - notification business rules
private final NotificationEssence essence;
// Realization layer - email, SMS, push notification services
private final EmailService emailService;
private final SMSService smsService;
private final PushNotificationService pushService;
public NotificationCapability(
EmailService emailService,
SMSService smsService,
PushNotificationService pushService
) {
this.essence = new NotificationEssence();
this.emailService = emailService;
this.smsService = smsService;
this.pushService = pushService;
}
@Override
public void initialize() {
// Initialize notification services
emailService.connect();
smsService.connect();
pushService.connect();
}
@Override
public void start() {
// Services are ready to send notifications
}
/**
* Send a notification through the appropriate channel
*/
public void sendNotification(Notification notification) {
// Validate using essence layer
ValidationResult validation = essence.validateNotification(notification);
if (!validation.isValid()) {
throw new InvalidNotificationException(validation.getErrors());
}
// Route to appropriate channel
switch (notification.getChannel()) {
case EMAIL:
emailService.send(
notification.getRecipient(),
notification.getSubject(),
notification.getMessage()
);
break;
case SMS:
smsService.send(
notification.getRecipient(),
notification.getMessage()
);
break;
case PUSH:
pushService.send(
notification.getRecipient(),
notification.getMessage()
);
break;
}
}
@Override
public Object getContractImplementation(Class<?> contractType) {
if (contractType == NotificationContract.Provision.class) {
return new NotificationProvisionImpl(this);
}
return null;
}
@Override
public void injectDependency(Class<?> contractType, Object implementation) {
// No dependencies
}
@Override
public void stop() {
// Stop accepting new notifications
}
@Override
public void shutdown() {
emailService.disconnect();
smsService.disconnect();
pushService.disconnect();
}
}
After extracting the Notification capability, other capabilities can use it through the NotificationContract rather than implementing their own notification logic. This reduces duplication and centralizes notification concerns.
Another important refactoring is splitting capabilities that have grown too large. As capabilities evolve, they sometimes accumulate too many responsibilities. When a capability becomes difficult to understand or test, it may need to be split into multiple smaller capabilities.
For example, suppose the Order Processing capability has grown to include not only order submission but also order fulfillment, shipping coordination, and returns processing. These are related but distinct concerns that could be separated into different capabilities. The team might refactor to create separate capabilities for Order Management, Fulfillment Management, and Returns Management, each with clear responsibilities and contracts.
Refactoring also focuses on improving the essence layer. As domain understanding deepens, the team refines the domain model to better reflect business concepts. Complex conditional logic might be replaced with polymorphism. Implicit business rules might be made explicit through domain objects.
/**
* Refactored essence layer using domain objects
* Replaces primitive obsession with rich domain model
*/
public class OrderProcessingEssence {
/**
* Discount policy using strategy pattern
* Replaces complex conditional logic
*/
public interface DiscountPolicy {
Money calculateDiscount(Money subtotal, Customer customer);
}
/**
* Volume discount for large orders
*/
public class VolumeDiscountPolicy implements DiscountPolicy {
private final Money threshold;
private final double discountRate;
public VolumeDiscountPolicy(Money threshold, double discountRate) {
this.threshold = threshold;
this.discountRate = discountRate;
}
@Override
public Money calculateDiscount(Money subtotal, Customer customer) {
if (subtotal.isGreaterThan(threshold)) {
return subtotal.multiply(discountRate);
}
return Money.zero(subtotal.getCurrency());
}
}
/**
* Loyalty discount for preferred customers
*/
public class LoyaltyDiscountPolicy implements DiscountPolicy {
private final double discountRate;
public LoyaltyDiscountPolicy(double discountRate) {
this.discountRate = discountRate;
}
@Override
public Money calculateDiscount(Money subtotal, Customer customer) {
if (customer.isPreferred()) {
return subtotal.multiply(discountRate);
}
return Money.zero(subtotal.getCurrency());
}
}
private final List<DiscountPolicy> discountPolicies;
public OrderProcessingEssence() {
this.discountPolicies = new ArrayList<>();
discountPolicies.add(new VolumeDiscountPolicy(Money.of(1000, "USD"), 0.10));
discountPolicies.add(new LoyaltyDiscountPolicy(0.05));
}
/**
* Calculate total with all applicable discounts
*/
public Money calculateTotal(OrderRequest request, Customer customer) {
Money subtotal = calculateSubtotal(request);
// Apply all discount policies
Money totalDiscount = Money.zero("USD");
for (DiscountPolicy policy : discountPolicies) {
Money discount = policy.calculateDiscount(subtotal, customer);
totalDiscount = totalDiscount.add(discount);
}
return subtotal.subtract(totalDiscount);
}
private Money calculateSubtotal(OrderRequest request) {
Money subtotal = Money.zero("USD");
for (OrderLine line : request.getOrderLines()) {
Money lineTotal = line.getUnitPrice().multiply(line.getQuantity());
subtotal = subtotal.add(lineTotal);
}
return subtotal;
}
}
This refactoring replaces complex conditional logic with a strategy pattern, making the discount calculation more flexible and easier to extend. New discount policies can be added without modifying existing code.
The realization layer also benefits from refactoring. As infrastructure integration grows more complex, the team introduces patterns such as repository pattern for data access, adapter pattern for external services, and circuit breaker pattern for resilience.
The result of continuous refactoring is a codebase that remains clean and maintainable even as it grows. The three-layer structure provides clear guidance for where different types of code belong. Contracts remain stable while implementations improve. Technical debt is addressed incrementally rather than accumulating until it becomes overwhelming.
DEPLOYMENT AND OPERATIONS IN CAPABILITY-CENTRIC SYSTEMS
Deployment and operations are integral parts of each sprint in modern agile development. Capability-Centric Architecture supports multiple deployment models and provides clear operational boundaries through capabilities.
Each capability can be deployed independently or as part of a larger deployment unit. The deployment descriptor specifies how a capability should be deployed, including resource requirements, scaling policies, and health check configurations.
/**
* Deployment descriptor for a capability
* Specifies deployment configuration independent of implementation
*/
public class DeploymentDescriptor {
private final String capabilityName;
private final DeploymentMode mode;
private final ResourceRequirements resources;
private final ScalingPolicy scaling;
private final HealthCheckConfig healthCheck;
public enum DeploymentMode {
EMBEDDED, // Deploy in same process as other capabilities
STANDALONE, // Deploy in separate process
CONTAINERIZED, // Deploy in container (Docker, etc.)
SERVERLESS // Deploy as serverless function
}
public DeploymentDescriptor(
String capabilityName,
DeploymentMode mode,
ResourceRequirements resources,
ScalingPolicy scaling,
HealthCheckConfig healthCheck
) {
this.capabilityName = capabilityName;
this.mode = mode;
this.resources = resources;
this.scaling = scaling;
this.healthCheck = healthCheck;
}
public String getCapabilityName() {
return capabilityName;
}
public DeploymentMode getMode() {
return mode;
}
public ResourceRequirements getResources() {
return resources;
}
public ScalingPolicy getScaling() {
return scaling;
}
public HealthCheckConfig getHealthCheck() {
return healthCheck;
}
}
The same capability implementation can be deployed in different modes depending on the environment and requirements. In development, capabilities might be deployed embedded in a single process for easy debugging. In production, capabilities might be deployed in separate containers for independent scaling and fault isolation.
For containerized deployment, the team creates Docker images for each capability and deployment descriptors for Kubernetes.
/**
* Kubernetes deployment manager for capabilities
* Handles containerized deployment and orchestration
*/
public class KubernetesDeploymentManager {
private final KubernetesClient k8sClient;
private final ContainerRegistry containerRegistry;
public KubernetesDeploymentManager(
KubernetesClient k8sClient,
ContainerRegistry containerRegistry
) {
this.k8sClient = k8sClient;
this.containerRegistry = containerRegistry;
}
/**
* Deploy a capability to Kubernetes cluster
*/
public void deployCapability(DeploymentDescriptor descriptor) {
// Build container image
String imageName = buildContainerImage(descriptor);
// Push to container registry
containerRegistry.push(imageName);
// Create Kubernetes deployment
createDeployment(descriptor, imageName);
// Create service for capability
createService(descriptor);
// Configure auto-scaling if enabled
if (descriptor.getScaling().isAutoScalingEnabled()) {
configureAutoScaling(descriptor);
}
}
private String buildContainerImage(DeploymentDescriptor descriptor) {
// Build Docker image for capability
String imageName = descriptor.getCapabilityName() + ":latest";
// Dockerfile is generated based on capability requirements
DockerfileGenerator generator = new DockerfileGenerator();
String dockerfile = generator.generate(descriptor);
// Build image
DockerBuilder builder = new DockerBuilder();
builder.build(dockerfile, imageName);
return imageName;
}
private void createDeployment(DeploymentDescriptor descriptor, String imageName) {
Deployment deployment = new Deployment();
deployment.setName(descriptor.getCapabilityName());
deployment.setReplicas(descriptor.getScaling().getMinReplicas());
deployment.setImage(imageName);
deployment.setResources(descriptor.getResources());
deployment.setHealthCheck(descriptor.getHealthCheck());
k8sClient.applyDeployment(deployment);
}
private void createService(DeploymentDescriptor descriptor) {
Service service = new Service();
service.setName(descriptor.getCapabilityName());
service.setType("ClusterIP");
service.setPort(8080);
k8sClient.applyService(service);
}
private void configureAutoScaling(DeploymentDescriptor descriptor) {
HorizontalPodAutoscaler hpa = new HorizontalPodAutoscaler();
hpa.setName(descriptor.getCapabilityName());
hpa.setMinReplicas(descriptor.getScaling().getMinReplicas());
hpa.setMaxReplicas(descriptor.getScaling().getMaxReplicas());
hpa.setTargetCPU(descriptor.getScaling().getTargetCPUUtilization());
k8sClient.applyHPA(hpa);
}
}
Operations activities include monitoring, logging, and incident response. Each capability exposes health check endpoints and metrics that operations teams use to monitor system health.
/**
* Health check implementation for a capability
* Provides operational visibility into capability status
*/
public class CapabilityHealthCheck {
private final CapabilityInstance capability;
public CapabilityHealthCheck(CapabilityInstance capability) {
this.capability = capability;
}
/**
* Check if capability is healthy and ready to serve requests
*/
public HealthStatus checkHealth() {
HealthStatus status = new HealthStatus();
status.setCapabilityName(capability.getName());
// Check if capability is initialized
if (!capability.isInitialized()) {
status.setStatus(Status.DOWN);
status.addDetail("Capability not initialized");
return status;
}
// Check if capability is started
if (!capability.isStarted()) {
status.setStatus(Status.DOWN);
status.addDetail("Capability not started");
return status;
}
// Check dependencies
for (String dependency : capability.getDependencies()) {
if (!isDependencyHealthy(dependency)) {
status.setStatus(Status.DEGRADED);
status.addDetail("Dependency " + dependency + " is unhealthy");
}
}
// Check resource availability
if (!hasAdequateResources()) {
status.setStatus(Status.DEGRADED);
status.addDetail("Resource constraints detected");
}
// If all checks passed
if (status.getStatus() == null) {
status.setStatus(Status.UP);
}
return status;
}
private boolean isDependencyHealthy(String dependency) {
// Check health of dependent capability
return true; // Simplified
}
private boolean hasAdequateResources() {
// Check memory, CPU, disk space
return true; // Simplified
}
}
The result of well-designed deployment and operations practices is a system that can be deployed continuously with confidence. Capabilities can be deployed independently, reducing deployment risk. Health checks provide visibility into system status. Monitoring and logging enable quick incident response. The clear boundaries provided by capabilities make it easier to understand and operate the system in production.
INTEGRATION OF ALL PHASES IN THE SPRINT CYCLE
All the activities described above integrate into a cohesive sprint cycle. Each sprint follows a consistent rhythm that includes requirements engineering, domain modeling, architecture baseline maintenance, stepwise refinement, testing, refactoring, and deployment.
The sprint begins with planning. The team reviews the product backlog and selects user stories to implement. Through requirements engineering activities, they identify which capabilities need to be created or enhanced and what contracts need to be defined or updated. They update the capability map and register new capabilities with the capability registry.
During the first days of the sprint, the team focuses on domain modeling. They conduct collaborative sessions to understand the domain concepts and business rules. They capture this understanding in the essence layer of each capability. They write unit tests for the essence layer to verify that the domain logic is correct.
As domain modeling progresses, the team begins implementing the realization layer. They integrate with databases, message queues, and external services. They write integration tests to verify that infrastructure integration works correctly. They implement the adaptation layer to provide interfaces for other capabilities and external systems.
Throughout the sprint, the team continuously tests their work. Unit tests run with every code change, providing immediate feedback. Integration tests run frequently to catch integration issues early. Contract tests verify that capabilities fulfill their obligations. End-to-end tests validate complete user scenarios.
Refactoring happens continuously as the team notices opportunities to improve the code. They extract duplicated logic into shared capabilities. They simplify complex essence layer code. They improve realization layer patterns. They ensure that the three-layer structure remains clear and that contracts remain stable.
Near the end of the sprint, the team prepares for deployment. They update deployment descriptors, build container images, and run deployment scripts. They verify that health checks work correctly and that monitoring is in place. They deploy to staging environments for final validation.
The sprint ends with a review and retrospective. The team demonstrates working software to stakeholders. They reflect on what went well and what could be improved. They update the architecture baseline based on what they learned. They plan for the next sprint.
The result of this integrated approach is predictable, sustainable delivery of valuable software. Each sprint delivers working, tested, deployable capabilities. The architecture remains clean and maintainable. Technical debt is addressed continuously. The team builds momentum and confidence as the system grows.
RESULTS AND ARTIFACTS OF EACH STEP
Each step in the capability-centric development process produces specific results and artifacts that guide subsequent work and provide documentation for the system.
Requirements engineering produces the capability map, which shows all capabilities in the system and their relationships. It produces contract definitions that specify the interfaces between capabilities. It produces quality attribute scenarios that describe non-functional requirements. It produces user story mappings that show how user needs map to capabilities.
Domain modeling produces the essence layer code, which captures pure business logic. It produces domain model diagrams that visualize concepts and relationships. It produces unit tests that verify domain logic. It produces ubiquitous language documentation that defines domain terms.
Architecture baseline establishment produces the capability registry, which tracks all capabilities and their dependencies. It produces the lifecycle manager, which controls capability initialization and shutdown. It produces deployment descriptors that specify how capabilities should be deployed. It produces architecture decision records that document important architectural choices.
Stepwise refinement produces working capability implementations that grow incrementally. It produces the realization layer code that integrates with infrastructure. It produces the adaptation layer code that provides external interfaces. It produces integration tests that verify infrastructure integration.
Testing produces comprehensive test suites at multiple levels. It produces unit tests for the essence layer that run in milliseconds. It produces integration tests for the realization layer that verify infrastructure integration. It produces contract tests that ensure interface compliance. It produces end-to-end tests that validate complete scenarios.
Refactoring produces cleaner, more maintainable code. It produces extracted capabilities that eliminate duplication. It produces simplified essence layer logic that better reflects the domain. It produces improved realization layer patterns that enhance performance and reliability.
Deployment and operations produce deployed capabilities running in production. They produce container images for containerized deployment. They produce Kubernetes configurations for orchestration. They produce health check endpoints for monitoring. They produce metrics and logs for operational visibility.
The cumulative result of all these activities is a system that delivers value to users while remaining maintainable and evolvable. The capability-centric approach provides clear structure without imposing rigidity. Teams can work independently on different capabilities while maintaining architectural coherence. The system can grow organically while preserving quality and integrity.
CONCLUSION
Designing applications with Capability-Centric Architecture in agile and lean development processes provides software engineers with a powerful framework for building complex systems incrementally. The approach aligns naturally with agile principles of iterative delivery, continuous feedback, and adaptive planning while providing the architectural structure needed for long-term maintainability.
Throughout each sprint, engineers conduct specific activities that build on each other to create cohesive, well-architected capabilities. Requirements engineering identifies capabilities and defines contracts. Domain modeling captures essential business logic in the essence layer. Architecture baseline establishment provides the infrastructure for managing capabilities and their dependencies. Stepwise refinement grows capabilities incrementally across sprints. Comprehensive testing ensures quality at multiple levels. Continuous refactoring maintains code cleanliness and architectural integrity. Deployment and operations practices enable continuous delivery to production.
The three-layer structure of capabilities, consisting of essence, realization, and adaptation, provides clear guidance for where different types of code belong. The essence layer contains pure domain logic that can be tested in isolation. The realization layer handles infrastructure integration. The adaptation layer provides interfaces to other capabilities and external systems. This separation of concerns makes capabilities easier to understand, test, and evolve.
Contract-based interaction between capabilities enables independent development and deployment. Capabilities can evolve internally without affecting their consumers as long as contracts remain stable. The capability registry prevents architectural violations such as circular dependencies. The lifecycle manager ensures proper initialization and shutdown sequences.
The result is a development process that delivers working software incrementally while maintaining architectural quality. Teams build momentum as they see capabilities come to life sprint by sprint. The system grows organically while preserving coherence. Technical debt is addressed continuously rather than accumulating. The architecture supports both current needs and future evolution.
By following the practices described in this article, software engineering teams can leverage Capability-Centric Architecture to build systems that are flexible, maintainable, and valuable, whether those systems are embedded devices, enterprise platforms, or anything in between.
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