Patterns: Implementing Self-Service in an SOA Environment

124 Patterns: Implementing Self-Service in an SOA Environment

򐂰 Acceptability of use for data transfer

XML is a standard way of putting information in a format that can be

processed and exchanged across different hardware devices, operating

systems, software applications, and the Web.

򐂰 Uniformity and conformity

XML gives you an common format that could be developed upon and is

accepted industry-wide.

򐂰 Simplicity and openness

Information coded in XML is human readable.

򐂰 Separation of data and display

The representation of the data is separated from the presentation and

formatting of the data for display in a browser or other device.

򐂰 Industry acceptance

XML has been accepted widely by the information technology and computing

industry. Numerous tools and utilities are available, along with new products

for parsing and transforming XML data to other data, or for display.

Disadvantages of XML

Some XML issues to consider are:

򐂰 Complexity

While XML tags can allow software to recognize meaningful content within

documents, this is only useful to the extent that the software reading the

document knows what the tagged content means in human terms, and knows

what to do with it.

򐂰 Standardization

When multiple applications use XML to communicate with each other they

need to agree on the tag names they are using. While industry-specific

standard tag definitions often do exist, you can still declare your own

nonstandard tags.

򐂰 Large size

XML documents tend to be larger in size than other forms of data

representation.

6.3.9 Enterprise JavaBeans

Enterprise JavaBeans is Sun Microsystem's trademarked term for its EJB

architecture, or

component model. When writing to the EJB specification, you are

developing enterprise beans or, if you prefer, EJBs for short.

Chapter 6. Technology options 125

Enterprise beans are distinguished from JavaBeans in that they are designed to

be installed on a server and accessed remotely by a client. The EJB framework

provides a standard for server-side components with transactional

characteristics.

The EJB framework specifies clearly the responsibilities of the EJB developer

and the EJB container provider. The intent is that the plumbing required to

implement transactions or database access can be implemented by the EJB

container. The EJB developer specifies the required transactional and security

characteristics of an EJB in a deployment descriptor (this is sometimes referred

to as declarative programming). In a separate step, the EJB is then deployed to

the EJB container provided by the application server vendor of your choice.

There are three types of Enterprise JavaBeans:

򐂰 Session beans

򐂰 Entity beans

򐂰 Message-driven beans

A typical session bean has the following characteristics:

򐂰 Executes on behalf of a single client.

򐂰 Can be transactional.

򐂰 Can update data in an underlying database.

򐂰 Is relatively short lived.

򐂰 Is destroyed when the EJB server is stopped. The client has to establish a

new session bean to continue computation.

򐂰 Does not represent persistent data that should be stored in a database.

򐂰 Provides a scalable runtime environment to execute a large number of

session beans concurrently.

A typical entity bean has the following characteristics:

򐂰 Represents data in a database.

򐂰 Can be transactional.

򐂰 Is shared access from multiple users.

򐂰 Can be long-lived, as long as the data in the database.

򐂰 Survives restarts of the EJB server. A restart is transparent to the client.

򐂰 Provides a scalable runtime environment for a large number of concurrently

active entity objects.

A typical message-driven bean has the following characteristics: