CAPABILITY-CENTRIC ARCHITECTURE (CCA) revisited: Car Charging System

The Core Concepts Of Capability-Centric Architecture (CCA)

Some weeks ago I published an article on Capability-Centric Architecture (http://stal.blogspot.com/2025/10/capability-centric-architecture-unified.html) that is designed as an extension of Clean Architecture and Hexagonal Architecture. 

Just to remind you: The Capability-Centric Architecture (CCA) is an innovative architectural pattern designed to bridge the traditional gap between the stringent demands of embedded systems, such as direct hardware access, real-time performance, and resource efficiency, and the requirements of enterprise systems, including flexibility, scalability, and rapid evolution. CCA extends established concepts from Domain-Driven Design, Hexagonal Architecture, and Clean Architecture, making it equally applicable to microcontrollers and cloud platforms. It provides a unified conceptual framework for effectively managing complexity, dependencies, and changes across diverse system landscapes.

The core concepts of CCA define its foundational principles. Capabilities are cohesive, value-delivering functional units that encapsulate a domain model, technical mechanisms, quality attributes, and an evolution strategy. Each Capability possesses an internal structure known as the Capability Nucleus, which comprises three distinct layers: the Essence, the Realization, and the Adaptation. The Essence layer contains the pure domain logic or algorithmic core, operating independently of infrastructure and highly testable. The Realization layer implements the technical mechanisms necessary to make the Essence functional in the real world, such as hardware access for embedded systems or database and message queue integration for enterprise systems. The Adaptation layer provides the interfaces through which the Capability interacts with other Capabilities or external systems.

Capability Contracts are crucial for defining what a Capability provides (Provisions), what it requires (Requirements), and the interaction patterns and quality attributes that govern its behavior (Protocols). These contracts enable independent evolution and interaction between Capabilities. Efficiency Gradients allow for the implementation of critical paths with minimal overhead, such as direct hardware access for real-time operations, while less critical paths can leverage higher abstractions for increased flexibility and maintainability. Evolution Envelopes describe how a Capability can evolve over time, including version information, deprecation policies, and migration paths.

Central mechanisms and advantages of CCA further enhance its utility. A Capability Registry manages Capabilities, their Contracts, and Bindings, preventing circular dependencies and enabling a topological sorting for system initialization. Deployment Descriptors facilitate flexible deployment models, such as embedded, standalone, containerized, or serverless, independently of the Capability's internal implementation. Comprehensive test strategies are supported by the layered separation, allowing for efficient unit tests for the Essence, integration tests for the Realization, and contract tests to verify interfaces. Furthermore, CCA supports the integration of modern technologies like AI/ML models, Big Data, Cloud Computing, and containerization as specialized Capabilities within the architecture.

Designing a New System with CCA: Steps for Architecture and Design

Designing a new system using the Capability-Centric Approach involves a structured process that systematically breaks down complexity and fosters modularity and evolvability.

Step 1: Domain Analysis and Capability Identification

The initial step involves a thorough domain analysis to understand the problem space comprehensively. This includes identifying the primary stakeholders, their needs, and the core business processes or system functions. From this understanding, cohesive, value-delivering functional units are identified and defined as Capabilities. These Capabilities represent distinct areas of responsibility within the system. For instance, in a car charging system, managing user accounts, processing payments, and controlling the physical charging process would each likely be identified as separate Capabilities.

Step 2: Defining Capability Contracts

Once Capabilities are identified, their contracts must be meticulously defined. A Capability Contract specifies three key aspects: its Provisions, its Requirements, and its Protocols. Provisions describe the services or data that a Capability offers to others. Requirements detail the services or data that a Capability needs from other Capabilities or external systems to fulfill its purpose. Protocols define the interaction patterns, communication mechanisms, and quality attributes, such as latency or throughput, that govern how Capabilities interact. These contracts act as formal agreements between Capabilities, enabling independent development and evolution while ensuring interoperability.

Step 3: Designing the Capability Nucleus

The internal structure of each Capability, known as the Capability Nucleus, is then designed with its three distinct layers: Essence, Realization, and Adaptation. The Essence layer is developed first, focusing solely on the core domain logic or algorithms, free from any infrastructure concerns. This ensures high testability and promotes a clear separation of concerns. The Realization layer then implements the technical mechanisms required to execute the Essence in its specific environment. This could involve database access, hardware drivers, or external API calls. Finally, the Adaptation layer defines the external interfaces through which the Capability exposes its Provisions and consumes its Requirements, translating between the internal domain model and external interaction formats.

Step 4: Establishing Efficiency Gradients

Efficiency Gradients are established by identifying critical paths within the system that demand high performance or real-time responsiveness. For these paths, the architecture is designed to minimize overhead, potentially allowing direct access to underlying hardware or optimized low-level implementations. For less critical paths, higher levels of abstraction are employed to prioritize flexibility, maintainability, and ease of change. This strategic application of varying levels of abstraction ensures that performance-critical aspects are optimized without sacrificing the overall system's adaptability.

Step 5: Planning Evolution Envelopes

Each Capability is designed with an Evolution Envelope, which outlines its anticipated lifecycle and how it can evolve over time. This includes defining versioning strategies, deprecation policies for older interfaces or functionalities, and clear migration paths for consumers of the Capability. By proactively planning for evolution, the system can gracefully accommodate changes, new features, and technological advancements without requiring extensive re-architecting.

Step 6: Implementing the Capability Registry and Deployment Descriptors

Finally, a Capability Registry is implemented to manage and discover Capabilities and their contracts across the system. This registry helps in resolving dependencies, preventing circular references, and facilitating the dynamic composition of the system. Concurrently, Deployment Descriptors are created for each Capability, specifying how it can be deployed in various environments, whether embedded, as a standalone application, within containers, or as serverless functions. This separation of deployment concerns from implementation details provides significant flexibility in operationalizing the system.

Example: Car Charging System with CCA

Let us consider a car charging system as an example, encompassing both enterprise and embedded components, to illustrate the application of CCA principles.

System Overview: Enterprise and Embedded Components

The car charging system consists of several key functionalities distributed across enterprise and embedded domains. The enterprise components handle user-facing interactions and backend operations such as user management, payment processing, charge scheduling, and system monitoring. These components typically run on cloud platforms or dedicated servers, prioritizing scalability, data persistence, and user experience. The embedded components are responsible for the direct control of the charging hardware, including charger control, vehicle communication, and local power management. These components operate within the charging station itself, demanding real-time performance, hardware interaction, and resource efficiency.

Identifying Core Capabilities

Based on the system overview, we can identify several core Capabilities:

1. User Authentication Capability (Enterprise): This Capability manages user accounts, handles login processes, and verifies user identities for access to charging services.
2. Payment Processing Capability (Enterprise): This Capability integrates with payment gateways, processes transactions, and manages billing for charging sessions.
3. Charge Scheduling Capability (Enterprise): This Capability allows users to pre-book charging slots, set preferred charging times, and optimize charging based on energy prices or grid conditions.
4. Charger Control Capability (Embedded): This Capability directly manages the physical charging process, including starting, stopping, and monitoring the flow of electrical power to a vehicle.
5. Vehicle Communication Capability (Embedded): This Capability handles the communication protocols between the charging station and the electric vehicle, exchanging information such as battery state, charging requirements, and status updates.
6. Power Management Capability (Embedded): This Capability locally manages the power distribution within the charging station, allocating power resources efficiently and ensuring grid stability.

Detailing a Specific Capability: Charger Control Capability (Embedded)

Let us delve deeper into the Charger Control Capability, an embedded component, to illustrate its design according to CCA principles.

Capability Name: ChargerControl

Description: The ChargerControl Capability is responsible for managing the physical charging process. This includes initiating charging sessions, safely terminating them, and continuously monitoring the charge flow and status to a connected vehicle.

Capability Contract:

The contract for the ChargerControl Capability defines its interactions with other system components:

• Provisions: These are the services that ChargerControl offers.
  • startCharging(vehicleId, chargeRate): This provision initiates a charging session for a specified vehicle identifier with a desired charge rate.
  • stopCharging(vehicleId): This provision terminates an active charging session for a given vehicle identifier.
  • getChargeStatus(vehicleId): This provision returns the current charge status, including parameters such as instantaneous power, charging duration, and total energy delivered, for a specific vehicle.
• Requirements: These are the services or data that ChargerControl needs from other Capabilities.
  • VehicleCommunication.receiveChargeRequest(vehicleId, chargeProfile): The ChargerControl Capability requires the ability to receive charge requests and detailed charge profiles from the VehicleCommunication Capability.
  • PowerManagement.allocatePower(chargeRate): The ChargerControl Capability needs to request and receive power allocation from the PowerManagement Capability to ensure safe and efficient power delivery.
• Protocols: These define the interaction characteristics.
  • Asynchronous communication is used for charge requests and status updates, allowing the system to handle multiple requests without blocking.
  • Real-time response is mandated for critical control commands, such as emergency stop or immediate power adjustments, to ensure safety and operational integrity.

Capability Nucleus Design:

The ChargerControl Capability's internal structure adheres to the Essence, Realization, and Adaptation layers.

• Essence (Core Logic): This layer contains the pure, infrastructure-agnostic logic for managing the charging process.

  // ChargerControlEssence.java
  public class ChargerControlEssence {
  
      /**
       * Calculates the optimal charging curve based on battery state and requested rate.
       * This logic is independent of specific hardware or communication protocols.
       *
       * @param batteryState A representation of the vehicle's battery state (e.g., SoC, temperature).
       * @param requestedRate The desired charging rate in kW.
       * @return An optimal charge profile (e.g., a series of current/voltage setpoints over time).
       */
      public ChargeProfile calculateOptimalChargeCurve(BatteryState batteryState, double requestedRate) {
          // Placeholder for complex battery management system (BMS) logic.
          // This would involve algorithms considering battery chemistry, degradation,
          // and thermal management to determine a safe and efficient charging profile.
          // For example, it might implement a constant current, then constant voltage (CC-CV)
          // charging strategy, or more advanced adaptive algorithms.
          System.out.println("Calculating optimal charge curve for " + batteryState + " at " + requestedRate + " kW.");
          // Example: Simple linear profile for demonstration
          return new ChargeProfile(requestedRate * 0.9, requestedRate, 0.1); // Start low, ramp up, hold
      }
  
      /**
       * Monitors real-time electrical parameters during charging.
       * This method processes raw sensor data but does not directly interact with hardware.
       *
       * @param current The instantaneous current reading from the charger.
       * @param voltage The instantaneous voltage reading from the charger.
       * @param temperature The instantaneous temperature reading from the battery or charger.
       * @return A consolidated ChargeMonitorData object.
       */
      public ChargeMonitorData monitorChargeParameters(double current, double voltage, double temperature) {
          // This method would perform data aggregation, filtering, and basic analysis
          // of the raw electrical parameters. It might detect anomalies or trends
          // without knowing how the data was acquired.
          System.out.println("Monitoring charge: Current=" + current + "A, Voltage=" + voltage + "V, Temp=" + temperature + "C.");
          return new ChargeMonitorData(current, voltage, temperature, current * voltage);
      }
  
      /**
       * Applies safety limits to prevent overcharging, overheating, or other hazardous conditions.
       * This logic defines the safety boundaries for the charging process.
       *
       * @param current The current flowing into the battery.
       * @param voltage The voltage applied to the battery.
       * @param temperature The battery or charger temperature.
       * @return True if parameters are within safe limits, false otherwise.
       */
      public boolean applySafetyLimits(double current, double voltage, double temperature) {
          // Defines the absolute safety thresholds based on electrical engineering principles
          // and battery specifications. This is critical for preventing damage and ensuring user safety.
          boolean currentSafe = current <= 200.0; // Max 200A
          boolean voltageSafe = voltage <= 500.0 && voltage >= 50.0; // 50-500V
          boolean tempSafe = temperature >= -20.0 && temperature <= 60.0; // -20 to 60C
          if (!currentSafe || !voltageSafe || !tempSafe) {
              System.err.println("Safety limit violation detected!");
              return false;
          }
          return true;
      }
  
      // Helper classes for demonstration
      public static class BatteryState {
          public double stateOfCharge; // 0.0 to 1.0
          public double temperature;
          // Constructor and getters/setters
          public BatteryState(double soc, double temp) {
              this.stateOfCharge = soc;
              this.temperature = temp;
          }
          @Override
          public String toString() {
              return "SoC: " + stateOfCharge + ", Temp: " + temperature;
          }
      }
  
      public static class ChargeProfile {
          public double initialRate;
          public double maxRate;
          public double rampTime;
          // Constructor and getters/setters
          public ChargeProfile(double initialRate, double maxRate, double rampTime) {
              this.initialRate = initialRate;
              this.maxRate = maxRate;
              this.rampTime = rampTime;
          }
          @Override
          public String toString() {
              return "Initial: " + initialRate + "kW, Max: " + maxRate + "kW, Ramp: " + rampTime + "s";
          }
      }
  
      public static class ChargeMonitorData {
          public double current;
          public double voltage;
          public double temperature;
          public double power;
          // Constructor and getters/setters
          public ChargeMonitorData(double current, double voltage, double temperature, double power) {
              this.current = current;
              this.voltage = voltage;
              this.temperature = temperature;
              this.power = power;
          }
          @Override
          public String toString() {
              return "Current: " + current + "A, Voltage: " + voltage + "V, Temp: " + temperature + "C, Power: " + power + "W";
          }
      }
  }
  

  The ChargerControlEssence class embodies the core logic. It includes methods like calculateOptimalChargeCurve which determines the best charging strategy based on battery conditions, monitorChargeParameters for processing raw sensor data into meaningful metrics, and applySafetyLimits to enforce critical safety thresholds. This code is designed to be highly testable and independent of any specific hardware or communication protocols, representing the pure domain knowledge of charging.

• Realization (Technical Mechanisms): This layer implements the specific technical mechanisms to make the Essence functional in the real-world embedded environment. It handles direct hardware interaction.

  // ChargerControlRealization.java
  public class ChargerControlRealization {
  
      private HardwareInterface hardware; // Interface for actual power electronics control
      private SensorReader sensorReader; // Interface for reading current, voltage, temp sensors
  
      public ChargerControlRealization(HardwareInterface hardware, SensorReader sensorReader) {
          this.hardware = hardware;
          this.sensorReader = sensorReader;
      }
  
      /**
       * Configures the power electronics to start charging at a given rate.
       * This method directly interacts with the hardware components.
       *
       * @param targetPowerKw The target power in kilowatts.
       */
      public void setChargingPower(double targetPowerKw) {
          // This would translate the target power into specific commands for the
          // power electronics, e.g., setting PWM duty cycles for a DC-DC converter.
          // It might involve converting kW to current/voltage setpoints based on system voltage.
          System.out.println("Realization: Setting charging power to " + targetPowerKw + " kW via hardware.");
          hardware.sendPowerCommand(targetPowerKw);
      }
  
      /**
       * Reads real-time data from physical sensors.
       *
       * @return An array of sensor readings (e.g., current, voltage, temperature).
       */
      public double[] readSensorData() {
          // Directly calls the sensor hardware interface to get raw data.
          double current = sensorReader.getCurrent();
          double voltage = sensorReader.getVoltage();
          double temperature = sensorReader.getTemperature();
          System.out.println("Realization: Reading sensor data: C=" + current + ", V=" + voltage + ", T=" + temperature);
          return new double[]{current, voltage, temperature};
      }
  
      /**
       * Stops the charging process at the hardware level.
       */
      public void stopHardwareCharging() {
          // Sends a command to the power electronics to safely shut down the charging current.
          System.out.println("Realization: Stopping hardware charging.");
          hardware.sendStopCommand();
      }
  
      // Mock interfaces for hardware interaction
      public interface HardwareInterface {
          void sendPowerCommand(double powerKw);
          void sendStopCommand();
      }
  
      public interface SensorReader {
          double getCurrent();
          double getVoltage();
          double getTemperature();
      }
  }
  

  The ChargerControlRealization class handles the low-level interactions. It takes HardwareInterface and SensorReader dependencies, which represent the actual physical hardware. Methods like setChargingPowertranslate abstract power requests into concrete hardware commands, while readSensorData directly fetches readings from physical sensors. This layer is highly coupled to the specific hardware but is isolated from the core logic in the Essence.

• Adaptation (Interfaces): This layer provides the necessary interfaces for the ChargerControl Capability to interact with other Capabilities and external systems.

  // ChargerControlAdapter.java
  public class ChargerControlAdapter {
  
      private ChargerControlEssence essence;
      private ChargerControlRealization realization;
      private VehicleCommunicationService vehicleCommService; // Dependency on another Capability's interface
      private PowerManagementService powerManagementService; // Dependency on another Capability's interface
  
      public ChargerControlAdapter(ChargerControlEssence essence,
                                   ChargerControlRealization realization,
                                   VehicleCommunicationService vehicleCommService,
                                   PowerManagementService powerManagementService) {
          this.essence = essence;
          this.realization = realization;
          this.vehicleCommService = vehicleCommService;
          this.powerManagementService = powerManagementService;
      }
  
      /**
       * Initiates a charging session. This is the public entry point for the Capability.
       * It orchestrates calls to Essence and Realization, and interacts with other Capabilities.
       *
       * @param vehicleId The ID of the vehicle to charge.
       * @param requestedRate The desired charging rate.
       * @return True if charging started successfully, false otherwise.
       */
      public boolean startCharging(String vehicleId, double requestedRate) {
          System.out.println("Adapter: Received request to start charging for " + vehicleId + " at " + requestedRate + " kW.");
  
          // 1. Communicate with VehicleCommunication Capability to get vehicle status
          ChargerControlEssence.BatteryState batteryState = vehicleCommService.getVehicleBatteryState(vehicleId);
          if (batteryState == null) {
              System.err.println("Adapter: Could not get battery state for " + vehicleId + ". Aborting.");
              return false;
          }
  
          // 2. Use Essence to calculate optimal charge profile
          ChargerControlEssence.ChargeProfile chargeProfile = essence.calculateOptimalChargeCurve(batteryState, requestedRate);
  
          // 3. Request power allocation from PowerManagement Capability
          boolean powerAllocated = powerManagementService.allocatePower(chargeProfile.maxRate);
          if (!powerAllocated) {
              System.err.println("Adapter: Power allocation failed for " + vehicleId + ". Aborting.");
              return false;
          }
  
          // 4. Use Realization to set hardware charging power
          realization.setChargingPower(chargeProfile.initialRate);
  
          // 5. Start monitoring loop (simplified for example)
          new Thread(() -> {
              while (true) { // In a real system, this loop would have proper termination conditions
                  double[] sensorData = realization.readSensorData();
                  ChargerControlEssence.ChargeMonitorData monitorData =
                          essence.monitorChargeParameters(sensorData[0], sensorData[1], sensorData[2]);
  
                  if (!essence.applySafetyLimits(monitorData.current, monitorData.voltage, monitorData.temperature)) {
                      System.err.println("Adapter: Safety limits violated. Stopping charging for " + vehicleId + ".");
                      stopCharging(vehicleId); // Self-correction
                      break;
                  }
                  // Report status to VehicleCommunication and/or Enterprise monitoring
                  vehicleCommService.reportChargeStatus(vehicleId, monitorData);
  
                  try {
                      Thread.sleep(1000); // Monitor every second
                  } catch (InterruptedException e) {
                      Thread.currentThread().interrupt();
                      break;
                  }
              }
          }).start();
  
          System.out.println("Adapter: Charging started successfully for " + vehicleId + ".");
          return true;
      }
  
      /**
       * Stops an ongoing charging session.
       *
       * @param vehicleId The ID of the vehicle to stop charging.
       * @return True if charging stopped successfully, false otherwise.
       */
      public boolean stopCharging(String vehicleId) {
          System.out.println("Adapter: Received request to stop charging for " + vehicleId + ".");
          realization.stopHardwareCharging();
          powerManagementService.releasePower(vehicleId); // Release allocated power
          System.out.println("Adapter: Charging stopped for " + vehicleId + ".");
          return true;
      }
  
      /**
       * Retrieves the current charging status.
       *
       * @param vehicleId The ID of the vehicle.
       * @return The current charge status data.
       */
      public ChargerControlEssence.ChargeMonitorData getChargeStatus(String vehicleId) {
          // In a real system, this would retrieve the latest monitored data for the specific vehicle.
          // For simplicity, let's just read current sensors.
          double[] sensorData = realization.readSensorData();
          return essence.monitorChargeParameters(sensorData[0], sensorData[1], sensorData[2]);
      }
  
      // Mock interfaces for inter-Capability communication
      public interface VehicleCommunicationService {
          ChargerControlEssence.BatteryState getVehicleBatteryState(String vehicleId);
          void reportChargeStatus(String vehicleId, ChargerControlEssence.ChargeMonitorData status);
      }
  
      public interface PowerManagementService {
          boolean allocatePower(double powerKw);
          void releasePower(String vehicleId);
      }
  }
  

  The ChargerControlAdapter acts as the public interface for the Capability. It orchestrates calls to the Essence for logic, the Realization for hardware control, and interacts with other Capabilities like VehicleCommunicationService and PowerManagementService through their defined interfaces. The startCharging method demonstrates a typical flow: fetching vehicle status, calculating a charge profile, requesting power, and then initiating hardware control and monitoring. This layer ensures that the internal complexity of the Capability is hidden, and interactions are standardized through its contract.

Efficiency Gradients:

For the ChargerControl Capability, efficiency gradients are clearly defined. Direct hardware access and low-latency control loops are implemented in the Realization layer for critical power control, ensuring immediate response to safety events or power adjustments. This represents a high-efficiency path. For less critical functions, such as logging historical charge data or reporting status to the enterprise monitoring system, higher-level abstractions and potentially slower, more flexible communication mechanisms are used. This balance optimizes performance where it is essential while maintaining flexibility elsewhere.

Evolution Envelopes:

The ChargerControl Capability is designed with an evolution envelope that anticipates future enhancements. Version 1.0 might support basic AC/DC charging. Version 1.1 could introduce support for the ISO 15118 communication standard, enabling smart charging features like Plug & Charge. Version 2.0 could then integrate Vehicle-to-Grid (V2G) capabilities, allowing the charger to not only draw power but also feed power back into the grid. Each version would have clear deprecation policies for older APIs and well-defined migration paths for systems consuming its services, ensuring backward compatibility where possible and smooth transitions otherwise.

Conclusion

The Capability-Centric Architecture provides a robust and flexible framework for designing complex systems that span both embedded and enterprise domains. By clearly defining Capabilities, their internal structure through the Nucleus (Essence, Realization, Adaptation), and their external interactions via Contracts, CCA enables modularity, independent evolution, and effective management of complexity. The car charging system example demonstrates how these principles can be applied to create a system that is both performant in its embedded components and flexible in its enterprise services, ensuring safety, scalability, and adaptability to future requirements. This architectural approach fosters a systematic way to build resilient and future-proof solutions in an increasingly interconnected world.