Choosing the Right Tool: Unveiling RAP vs. CAP in Software Development (EN)

Software Development: RAP vs. CAP

In the dynamic landscape of software development, the choice between programming approaches can significantly impact project outcomes. Staying ahead in software development requires not only mastering modern technologies but also understanding the most effective methodologies. We will introduce ABAP RESTful Application Programming Model (RAP) and SAP Cloud Application Programming Model (CAP), two well-known competitors in this field, who each provide distinctive approaches with certain benefits and limitations.

The following article includes a detailled presentation of the two frameworks. From their origins to their practical applications, we will highlight the strengths and weaknesses of each approach and provide developers with valuable insights into the ever-changing world of coding.

Having a deeper understanding of the two approaches will enable to make informed decisions in software development implementations.

RAP

The ABAP RESTful Application Programming Model (RAP) defines the architecture for efficient end-to-end development of intrinsically SAP HANA-optimized OData services, such as Fiori apps. It offers developers an efficient way to build enterprise-ready, SAP HANA-optimized, OData-based Fiori UI services and Web APIs.

RAP Architect Overview

Main development tasks:

Data modelling & Behaviour:

  • The data model comprises the description of the different entities involved in a business scenario, for example travel and booking application, and their relationships, parent-child relationship between travel and booking.
  • CDS Views are big strength for SAP RAP.
  • The behaviour of the data model determines the actions that could be performed on it, it includes the ability to create, update or delete the data. This can be implemented by SAP RAP.

Business Service Definition:

  • A business service definition (short form: service definition) describes which CDS entities of a data model are to be exposed so that a specific business service, for example, Sales Order handling, can be enabled.     
  • A service definition represents the service model that is generically derived from the underlying CDS-based data model.
  • the service definition is to define which data is to be exposed as a business service using one or more service bindings. A service definition itself is independent from the version or type of the protocol that is used for the business service.

Service Consumption:

  • A business object exposed as an OData UI service is consumable, for instance, by an SAP Fiori Elements app. Every front-end configuration, which is manifested in the back-end development object (for example, UI annotations), is exposed within the metadata of the service. That means, a Fiori UI reads the information in the metadata and creates the matching UI for the service. These UI settings can be enhanced and overwritten in the SAP Web IDE.
  • A UI service can be previewed with the Fiori Elements preview in the service binding tool. The preview mocks a real UI app and has the same look and feel as a Fiori Elements app. It is therefore a powerful tool to test the UI of your OData service already in the backend.

CAP

The SAP Cloud Application Programming Model (CAP) is a framework designed for building enterprise-grade services and applications.

It includes a collection of languages, libraries, and tools tailored to facilitate development. Core Data Services (CDS) is used as a universal modeling language for both domain models and service definitions. Nevertheless, in practical scenarios, a complex data model alone isn’t always adequate. Many business cases necessitate business logic complementing the model. The CAP framework provides Service SDKs and runtimes for Node.js and Java, furnishing libraries for service implementation and consumption, along with generic provider implementations that handle numerous requests automatically. All of these components aim to streamline implementation as easy as possible.

SAP Tools & Technologies

Main development tasks:

Domain Modeling:

  • Domain Models encapsulate the static, data-centric facets of a problem domain using entity-relationship models. They form the foundation for persistence models implemented in databases and service definitions.
  • CDS emphasizes conceptual modeling, aiming to capture intent rather than imperative implementations. This means focusing on “What” rather than “How”. This approach not only maintains the conciseness and comprehensibility of domain models but also enables the provision of optimized generic implementations.

Providing Services:

  • In a CAP application, services are typically defined within CDS models and operated by CAP runtimes. Every functional element within CAP constitutes a service, encapsulating the behavioral dimensions of a domain through exposed entities, actions, and events.
  • The CAP runtimes offer numerous generic implementations, which serve most requests automatically, with out-of-the-box solutions to recurring tasks such as search, pagination, or input validation – all generic features.
  • As most standard tasks and use cases are covered by generic service providers, the remaining cases that need custom handlers, reduce to real custom logic, specific to your domain and application.

Consuming Services:

  • If you want to use data from other services or you want to split your application into multiple microservices, you need a connection between those services. It’s called remote services. As everything in CAP is a service, remote services are modeled the same way as internal services — using CDS.
  • As everything in CAP is a service, remote services are modeled the same way as internal services — using CDS.
  • CAP supports service consumption with dedicated APIs to import service definitions, query remote services, mash up services, and work locally as much as possible.

Serving UIs:

  • You can consume the provided services, for example, from UI frontends. CAP provides out-of-the-box support for SAP Fiori UIs, for example, with respect to SAP Fiori annotations and advanced features such as search, value helps and SAP Fiori Draft. If flexibility and total customization for the UIs are required, CAP also offers another support option with Fiori Freestyle.

Comparison

In order to create a deeper understanding, we offer a comparison of both development approaches and a clear presentation of the strengths and weaknesses as well as the programming language and the development environment.

Choosing between RAP & CAP

If you are still facing the dilemma of selecting the right framework for your project the following chapter can be helpful. Let’s examine when to employ CAP and when to choose RAP in order to simplify the decision-making process.

When to use RAP?

  1. Integration with S/4HANA or broader Cloud Integrations: If your solution requires extensive integration with SAP S/4HANA or broader cloud ecosystems, RAP emerges as the preferred choice. Its capabilities extend to deep and direct integration with S/4HANA systems and support for complex, transactional logic.
  2. Utilization of Business Objects (BO): RAP introduces the concept of Business Objects (BO), making it the framework of choice when SAP business objectives need to be addressed. Leverage RAP’s BO capabilities to streamline business processes and enhance efficiency.
  3. On-Premises Deployment or ABAP Cloud Environment: RAP shines in scenarios where on-premises deployment is necessary. Additionally, for deployments in the ABAP cloud environment, RAP offers robust support for cloud-based implementations, ensuring flexibility in deployment choices.

When to use CAP?

  1. SAP Ecosystem Integration: If your organization operates within the SAP ecosystem, CAP offers seamless integration capabilities. Whether it’s SAP S/4HANA, SAP ERP, or SAP Cloud Platform services, CAP ensures smooth connectivity, enabling effortless interaction with SAP solutions.
  2. Rapid Application Development: Time-to-market is paramount, and CAP rises to the challenge with its out-of-the-box solutions and best practice guidance. Accelerate development timelines by leveraging CAP’s pre-built features and functionalities, reducing implementation efforts.
  3. Cloud-Native Applications: For those venturing into the realm of cloud-native applications, CAP aligns perfectly with modern cloud development principles. Built to thrive on platforms like SAP BTP, CAP offers scalability, resilience, and agility essential for cloud deployments.

In conclusion, the decision between RAP and CAP depends on the specific requirements and context of your project. By understanding the strengths and use cases of each framework, you can make an informed choice that aligns with your organization’s goals and objectives.

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