EclipseLink/UserGuide/SDO/Introduction to SDO (ELUG)

This section introduces concepts of Service Data Objects (SDO) and provides general information on it.

What Is SDO?

SDO is designed to be a unified view of data, much like the POJO is in Java EE. There are several programming languages (of which Java is one) that support the SDO specification.

You can use SDO to develop data-oriented applications. SDO includes an architecture and API.

The following are possible expressions of SDO:

• Dynamic Object Model
• Typed Object Model
• XML Representation
• Disconnected Object

For more information, see ...

Dynamic Object Model

SDO metadata is represented as Type and Property objects. A Type is comparable to a Java class, and a property to a Java field. This metadata is defined at run time either programmatically or from an XML schema, as follows:

Type customerType = TypeHelper.INSTANCE.getType(“urn:example”,  “customer”);
Property firstNameProperty = customerType.getProperty(“first-name”);

Type addressType = TypeHelper.INSTANCE.getType(“urn:example”, “address”);

Data is represented as instances of Types called DataObjects, these correspond to objects in Java. DataObjects have many generic accessors that can be used to manipulate the data.

DataObject customerDO = DataFactory.INSTANCE.create(customerType);
customerDO.setString(firstNameProperty, “Jane”);
 
DataObject addressDO = DataFactory.INSTANCE.create(“urn:example”, address);
addressDO.set(“street”, “123 Any Street”);

Typed Object Model

SDO as dynamic object models is useful in certain frameworks (dynamic models allow metadata to be added without requiring a redeployment of the application), but in other situations a strongly typed model is required (typed models allow for code completion in an IDE). A code generation step can be performed to produce typed interfaces complete with bean style accessors.

Customer customerDO = (Customer) DataFactory.INSTANCE.create(customerType);
CustomerDO.setFirstName(“Jane”);

XML Representation

SDO has built in support for handling XML. The SDO metadata can be introspected to determine what the corresponding XML representation is.

XSDHelper.INSTANCE.isMixed(customerType);
XSDHelper.INSTANCE.isElement(firstNameProperty);

The DataObjects themselves can then be converted to and from XML.

XMLHelper.INSTANCE.save(customerDO, “urn:example”, “customer”, System.out);

Disconnected Object

SDO was designed to represent disconnected data in a SCA (Service Component Architecture) environment. The main mechanism for accomplishing this goal is the ChangeSummary which tracks changes made to data objects over time (for DataObjects that have a ChangeSummary property).

List changed = customerDO.getChangeSummary().getChangedDataObjects();

EclipseLink is focussed on separating data from its messaging or persisted representations. Now with SDO support this data can be a POJO or a DataObject. This allows you to work with data in both Java EE and SCA environments.