Chapter 10: Introduction to SDO

Overview

The computer industry created a variety of solutions (languages, data-storage systems, transfer protocols) to fulfill similar needs. It is now developing technologies to mask the complexity of what's been created. The issue is being addressed because complexity is expensive, increasing the costs of training, development, and testing; and because complexity is confusing, reducing the quality of work.

Like SCA, Service Data Objects (SDO) is a response to complexity and is a proposed standard that is likely to gain the approval of a major standards organization. SDO, however, is a technology for representing data in a consistent way, even if the data comes from different kinds of sources.

When you work with SDO, you write code

• to create one or more structures called Data Objects, each of which includes business data organized into a collection of named properties.

• to get or set the data for each property, whether the property holds a data item such as a customer ID or a reference to another Data Object. Properties that hold data items are based on data types such as Boolean or Integer.

In fulfilling SDO-related tasks, you use the same syntax (the same application programming interface, or API) regardless of whether In relation to SOA, SDO allows for changes in the messages passed between services but does not require that those changes affect the service interface. In other words, the kind of interface is document rather than remote procedure call. If your company adds new functionality to the service, changes to the requester can occur over time (in many cases) rather than in urgent response to the upgrade.

• the data comes from a relational database, an XML file, a message queue, or some other source; or

• the data is created in the code, in accordance with a description such as an XML Schema definition.

SDO supports Java, C++, and PHP and is expected to support C, COBOL, and other languages.

Although companies have implemented early versions of SDO, the situation of interest to this book is that eighteen companies are in the Open Service Oriented Architecture (OSOA) collaboration, which is creating a set of SDO proposals for a major standards body to adopt. Our description in this chapter is based primarily on the OSOA document Service Data Objects for Java Specification Version 2.1.0. The current, publicly available proposals are at the following Web site: http://www.osoa.org.

Under the auspices of the Apache Software Foundation, the Tuscany incubator project is developing an open-source implementation of SCA and SDO. For details and code, see the following Web sites: http://incubator.apache.org/tuscany and http://www.apache.org.