The movement from SOAP-based web services towards RESTful-based web services is another evolutionary journey for PowerBuilder developers and their related applications. Originally, Sybase added SOAP (Simple Object Access Protocol)-based features in PowerBuilder version 8.0. The original SOAP features were aligned with the Java implementation of EasySOAP and provided a messaging protocol specification for exchanging structured information in the implementation of web services across computer networks. Sybase enhanced the web service feature in PowerBuilder version 9.0 to include the ability to handle more complex SOAP interactions. In PowerBuilder version 11.0, Sybase then added support for Microsoft’s .NET-based web service framework as well. This greatly improved the web service interaction possibilities in that era of PowerBuilder. The .NET web service feature was tweaked again in PowerBuilder version 11.5 (and latter PowerBuilder versions) to support the newer releases of the .NET framework.

Since PowerBuilder 11.5 though, the basic SOAP-based architecture has been PowerBuilder’s “go to” vehicle for web service interactions. However, the IT industry moved onward with newer REST (Representational State Transfer) web service technology, which has now become a de facto architectural style used by most modern web services. The REST approach defines a set of constraints and properties based on the HTTP protocol that provides greater interoperability between computer systems on the Internet today. By REST using a stateless protocol and standard operations, REST systems can have faster performance, reliability, and the ability to grow, by re-using components that can be managed and updated without affecting the system, even while it is running.

There are six guiding constraints that define a RESTful system. These constraints restrict the ways that the server may process and respond to client requests so that, by operating within these constraints, the service gains performance, scalability, simplicity, modifiability, visibility, portability, and reliability. If a service violates any of the required constraints, it cannot be considered RESTful. The formal REST constraints are as follows:

Client–server architectureStatelessnessCache-abilityLayered systemCode on demandUniform interface

The focus of a RESTful service is on resources and how to provide access to these resources. A resource can easily be thought of as an object as in OOP (object-oriented programming). A resource can consist of other embedded resources as well. While designing a system, the first thing to do is identify the resources and determine how they are related to each other. This is like the first steps of designing a database: identify entities and relations. Once we have identified our resources, the next thing we need is to find a way to represent these resources in our system. You can use any format for representing the resources, as REST does not put a restriction on the format of a representation.

The client and service talk to each other via messages. Clients send a request to the server, and the server replies with a response. Apart from the actual data, these messages also contain some metadata about the message. It is important to have some background about the HTTP request and response formats for designing RESTful Web services. REST requires each resource to have at least one URI (Uniform Resource Identifier). A RESTful service uses a directory hierarchy like human readable URIs to address its resources. The job of a URI is to identify a resource or a collection of resources. The actual operation is determined by an HTTP verb. The URI should not say anything about the operation or action. This enables us to call the same URI with different HTTP verbs to perform different operations.