This aligns with the service-oriented principle of Standardized Service Contract and the goal of promoting loose coupling and long-term evolvability. A technology-agnostic contract (e.g., based on a standard like OpenAPI) prevents the service implementation from being tightly bound to a specific technology stack, allowing for future replacement or consumption by diverse clients.

This creates tight coupling, as the Order Processing service is now directly dependent on the internal data schema and implementation of the Inventory service. A change in the Inventory database would break the Order Processing service. Loose coupling mandates that services interact only through published, stable contracts, not through shared databases or internal implementation details.

This describes the creation of a task service or process service, which is a standard service composition pattern. The parent service (the composition controller) orchestrates the sequence, preserving the autonomy and reusability of the underlying Inventory Check and Payment Processing utility services. It centralizes the business process logic without creating dependencies between the composed services.

The principle of Service Abstraction dictates that a service’s contract should hide its underlying logic, but also that its capabilities should be abstract and generic, not overly customized for specific consumers. By tailoring the single service for multiple specific consumers, they violated abstraction, creating a ‘swiss army knife’ service. A better approach might have been to keep the core service generic and create separate, composed services or facade layers for the application-specific variations.

Agnostic logic is the core characteristic of a reusable service. It means the service’s capabilities are derived from a broad, cross-cutting business entity (like ‘Customer’) or function (like ‘Validation’), rather than being designed for the needs of a single parent business process. This general-purpose nature is what enables its reuse across different applications and compositions.

Effective Service Discoverability requires metadata that caters to both humans and automated tools. A cryptic name and a purely technical description fail to communicate the business meaning and functionality of the service. To be truly discoverable, the registry entry should include a clear business name, a functional description of what it does (e.g., ‘Calculates sales tax for North American jurisdictions’), and its supported capabilities, enabling others to assess its relevance for their needs.

The Statelessness principle advocates for minimizing resource consumption by not retaining state in service instances. For a service that *must* manage state, the principle is applied by externalizing that state to a dedicated, scalable data store. This allows the service instances themselves to be disposable, scalable, and load-balanced, as any instance can retrieve the necessary state from the shared store to process a request.

This practice is central to maintaining loose coupling and composition autonomy in a evolving ecosystem. Service versioning (e.g., in the endpoint URL or contract namespace) allows consumers (like the parent composition) to migrate to a new version on their own schedule. Running multiple versions concurrently prevents forced, synchronized upgrades and minimizes disruption, a key aspect of service-oriented evolution.

Finer-grained services are more likely to be reusable (e.g., ‘Customer Identity’ could be used by many systems, while a monolithic ‘Customer’ service might be too specific). They also promote autonomy, as each can be developed, deployed, scaled, and changed independently. A large, coarse-grained service often becomes a monolithic entity that is difficult to reuse in part and whose components cannot evolve autonomously.

This aligns with the service-oriented principle of Standardized Service Contract and the goal of promoting loose coupling and long-term evolvability. A technology-agnostic contract (e.g., based on a standard like OpenAPI) prevents the service implementation from being tightly bound to a specific technology stack, allowing for future replacement or consumption by diverse clients.0