11.2 The Goals of TAU.NET System Design
11.2.1 Cell Systems
Before joining TAU, each member agency runs its business using a proprietary system of its own. We call these local agency systems the Cell Systems. The Cell Systems are heterogeneous in nature; they may be different in terms of system design, data structure, data storage, and user interface.
Each desired TAU functionality must be implemented as an extension of the Cell Systems. That is, there should be no central server in the TAU system. The Cell Systems, with the support of the TAU extensions, interact over the Internet to fulfill the goal of the distributed system. The TAU extensions are discussed in Section 11.2.4.
11.2.2 Information Exchange
Due to the heterogeneity of the Cell Systems, the distributed functions have to be supported by information exchange between their data storages. A standard data format is needed in order for the Cell Systems to share information. XML serves as an ideal vehicle to carry such information over the Internet.
11.2.3 Remote Services
In a distributed environment without a central server, each Cell System is extended to provide remote services over the Internet. These services allow the Cell System to communicate with its partner Cell Systems in order to exchange information that supports the distributed functions. Web Services are the natural choice for this purpose.
11.2.4 TAU.NET Node
A TAU.NET node is the extension for the Cell System of a participant agency, through which the Cell System joins the network of TAU. The Cell Systems communicate with each other via their TAU.NET nodes.
Communication between the TAU.NET nodes is based on Web Services. On the one hand, the TAU.NET acts as a server supplying Web methods with a standard interface. On the other hand, the TAU.NET node serves as a client supplying proxies whereby the remote Web methods can be called. In other words, the TAU.NET nodes constitute a middle tier that hooks the Cell Systems of the participant agencies so as to form an integral distributed system.
Figure 11-2 illustrates the concepts of TAU.NET Node and TAU.NET members.
Figure 11-2 Concept of TAU.NET.