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   Introducing the BEA Tuxedo System

The BEA Tuxedo system uses an operation called data-dependent routing to enable a client to send requests for the same service to multiple copies of that service. Which copy of the service eventually accepts and processes the request is determined by the data in the request message. Once an administrator has set up data-dependent routing for an application, client requests can be routed automatically to servers based on the data in the requests.

When an application includes multiple copies of the same service, each copy is assigned a unique purpose, just as the first volume of a multivolume encyclopedia contains entries that begin withe the letter "A." A list of all copies of the service, along with identifying information about the purpose of each, is kept in a set of routing tables in the BEA Tuxedo bulletin board. When the system receives a client request, it finds an identifying string in the request message and searches the routing tables in the bulletin board for the same string. On the basis of this match, the system identifies the appropriate server to which it can forward the client request.

Note: The bulletin board routing tables can be modified as necessary.

Data-dependent routing is useful when clients issue service requests to:

• Horizontally partitioned databases

• Rule-based servers

• Distributed Application

A horizontally partitioned database is an information repository that has been divided into segments, each of which is used to store a different category of information. This arrangement is similar to a library in which each shelf of a bookcase holds books for a different category (for example, biography, fiction, and so on).

Suppose two clients in a banking application issue requests for the current balance in two accounts: Account 3 and Account 17. If data-dependent routing is being used in the application, then the BEA Tuxedo system performs the following actions:

1. Gets the account numbers for the two service requests (3 and 17).

2. Checks the routing tables on the BEA TUXEXDO bulletin board that show which servers handle which range of data. (In this example, server 1 handles all requests for accounts 1 through 10; server 2 handles all requests for accounts 11 through 20.)

3. Sends each request to the appropriate server. Specifically, the system forwards the request about Account 3 to server 1, and the request about account 17 to server 2.

The following figure illustrates this process.

Example of Data-dependent Routing with Rule-based Servers

A banking application includes the following rules:

• Customers can withdraw up to $500 without entering a special password.

• Customers must enter a special password to withdraw more than $500.

Two clients issue withdrawal requests: one for $100 and one for $800. If data-dependent routing is enabled to support the withdrawal rules, then the BEA Tuxedo system performs the following actions:

Example of Data-dependent Routing with Distributed Application

The following diagram shows how client requests are routed to servers. In this example, a banking application called bankapp uses data-dependent routing. bankapp has three server groups (BANK1, BANK2, and BANK3) and two routing criteria (Account ID and Branch ID). The services WITHDRAW, DEPOSIT, and INQUIRY are routed using the Account_ID field; the services OPEN and CLOSE are routed using the Branch_ID field.

In the preceding diagram, requests are routed as indicated in the following table.

Withdrawals, Deposits, Inquiries, and Openings or Closings of the Following Accounts . . .	Are Routed to . . .
Numbers 10000-49999 for branches 1-4	Bank1
Numbers 50000-79999 for branches 5-7	Bank2
Numbers 80000-109999 for branches 8-10	Bank3