Requirements Modelling and Specification for Service Oriented Architecture

1.5. Technology Drivers

One of the historical drivers that led up to the widespread interest in SOA was the need to get disparate legacy and newer systems to interoperate or be accessed through a single login. This is the so-called Enterprise Application Integration (EAI). Typically, a large organization would, over the years, have accumulated a goulash of departmental systems and systems transferred through mergers and acquisitions. To link these together various point-to-point connexions would have been established, usually based on the interchange of comma-delimited files over batch tape or FTP links. The resulting spaghetti connexions are suggested by Figure 1-10.

Various technologies have been advanced to address this problem including object request brokers (ORBs) based on the CORBA standard (Common Object Request Broker Architecture) and message-oriented middleware (MOM). The main difference between the two is that ORBs deal with messages synchronously and MOM does so asynchronously. In plainer terms, in an ORB environment, an application sends a message to another application and waits for a reply. If the systems crash, everything will have to start all over again. With MOM, such messages are placed on a queue for delivery and, if necessary, the sending application can carry on with its business. Usually, eventual delivery of the message is guaranteed by the middleware. Some modern MOM products also include ORB capabilities.

Figure 1.10. Enterprise spaghetti.

Typical ...