Client Application Developer's Guide
|
 |
 |
|
 |
 |
This chapter introduces you to developing BEA Liquid Data for WebLogic® client applications. It covers the following topics:
BEA Liquid Data for WebLogic is a data services platform product that significantly simplifies how client applications access and use data. In a typical organization, data comes from a variety of sources, including distributed databases, files, applications from partners or e-commerce exchange markets. With Liquid Data, client applications can use heterogeneous data through a unified service layer without having to contend with the complexity of working with distributed data sources using various connection mechanisms and data formats.
Liquid Data provides a uniform, consolidated interface for accessing and updating heterogeneous back-end data. It enables a services-oriented approach to information access using data services.
From the perspective of a client application, a data service typically represents a distinct business entity, such as a customer or order. Behind the scenes, the data service may aggregate the data that comprises a single view of the data, for example, from multiple sources and transform it in a number of ways. A data service may be related to other data services, and it is easy to follow these relationships in Liquid Data. Data services insulate the client application from the details of the composition of each business entity. The client application only has to know the public interface of the data service.
This document describes how to create Liquid Data-aware client applications. It explains the various client access mechanisms that Liquid Data supports and its main client-side data programming model, including Service Data Objects (SDO). It also describes how to create update-capable data services using the Liquid Data update framework.
A Liquid Data client is any process that consumes data services from Liquid Data. A client application may be, for example, a Java program, non-Java programs such as .NET applications, BEA WebLogic Workshop applications, or JDBC/ODBC clients.
As illustrated in Figure 1-1, Liquid Data supports several access mechanisms:
Whatever the client type, Liquid Data gives developers a uniform, services-oriented mechanism for accessing and modifying heterogeneous data from external sources. Developers can focus on the business logic of the application rather than details of various data source connections and formats.
Figure 1-1 Accessing Liquid Data Services
Developers can choose from several models for accessing Liquid Data services. The model chosen will depend on the access mechanism you decide to used. The possible access methods are:
Each access method has its own advantages and use. Table 1-2 provides a description of each of these access methods and summarizes the advantages of the various models for accessing Liquid Data services.
|
A Java interface for using data services. Returns data as data objects, providing full support for Service Data Objects (SDO) programming. For more information, see Accessing Data Services from Java Clients. |
|
|
|
A WebLogic Workshop control for accessing Liquid Data resources. For more information, see Accessing Data Services from Workshop Applications. |
|
|
|
A data service can be wrapped as a Web service, providing the data service with the benefits of web service features. For more information, see Exposing Data Services through Web Services. |
||
|
Client applications can use JDBC or ODBC to access Liquid Data services using SQL queries. The Liquid Data JDBC driver supports SQL-92. For more information, see Using the Liquid Data JDBC Driver. |
Service Data Objects (SDO), a specification proposed jointly by BEA and IBM, is a Java-based architecture and API for data programming. SDO unifies data programming against heterogeneous data sources. It simplifies data access, giving data consumers a consistent, uniform approach to using data whether it comes from a database, web service, application, or any other system.
SDO uses the concept of disconnected data graphs. Under this architecture, a client gets a copy of externally persisted data in a data graph, which is a structure for holding data objects. The client operates on the data remotely; that is, disconnected from the data source. If data changes need to be saved to the data source, a connection to the source is re-acquired. Holding connections and locks the data at the source for the minimum time possible in this way maximizes the scalability and performance of applications.
To SDO clients, the data has a uniform appearance no matter where it came from or what its source format is. Enabling this unified view of data in the SDO model is the Data Service Mediator. The mediator is the intermediary between data clients and back-end systems. It allows clients to access data services and invoke their functions to acquire data or submit data changes. Liquid Data serves as such a SDO mediator.
On the client side, information takes the form of data objects. Data objects are the basic unit of information prescribed by the SDO architecture. SDO has both static (or strongly typed) and dynamic (or loosely typed) interfaces for working with data objects.
Static interfaces provide a programmer-friendly model for getting and setting properties in a data object. Accessors are generated for each property in the data type of a data service, for example getCustomerName() and setCustomerName() for a Customer data object. The dynamic interface, on the other hand, is useful when a predefined static interface is unknown or undefined at runtime. Dynamic interface calls are in the form get("CustomerName") and set("CustomerName", "J. Dough").
In keeping with the goals of a service-oriented architecture (SOA), data graphs are self-describing. The metadata API enables applications, tools, and frameworks to inspect information on the data contained in a data graph. The data is described by an XML schema, which describes the names of properties, their types, and more.
For details on using SDO, see Client Programming with Service Data Objects (SDO).
There are several steps you will take to when developing your application:
A prior or possibly parallel task is creation of Liquid Data services and their functions, which are accessed by client applications. Development of these entities is described in the Data Services Developer's Guide.
Liquid Data administrators can control access to deployed Liquid Data resources through role-based security policies. Liquid Data leverages and extends the security features of the underlying WebLogic platform. Roles can be set up in the WebLogic Administration Console. (Refer to the Liquid Data Administration Guide for information about the Administration Console.)
Access policies for Liquid Data resources can be defined at any level— on all data services in a deployment, individual data services, individual data service functions, or even on individual elements returned by the functions of a data service.
For complete information on WebLogic security, see:
The Liquid Data API includes the packages listed in Table 1-3.
SDO gives client applications create, read, update, and delete access to external data. Changes to data object property values can be persisted to back-end data sources. The programming details associated with data changes are hidden from the client. The client can update data in several heterogeneous, distributed sources with a single update call.
Liquid Data makes it easy to create data services that can apply changes to information as well as access from back-end data sources. For relational data sources, Liquid Data propagates the updates to the back-end source automatically. For non-relational sources, such as web services, or when you want to customize relational updates, Liquid Data provides an update framework that you can use to implement your own data source updates.
For details on using SDO to update data, see Enabling SDO Data Source Updates.
|
|
|
