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Transaction Managers

Transaction managers (TM) are designed to work within environments in which high availability and guaranteed transaction completion are important. The most common environment for these types of products are banking and financial applications.

TM products for most platforms are usually available through the hardware vendors themselves. Examples of these types of products include Encina, Tuxedo, and TOP END. Although TM products could be said to be data base connectivity types of products, some (e.g., Encina) use DCE features. Thus, they can be described as being more complete client/server products than products such as Microsoft’s ODBC or Borland’s IDAPI. Transaction-processing managers are used in heterogeneous distributed client/server environments to support the following:

  Global transactions that have an impact on multiple distributed data bases, including rollback for backup and recovery of global transactions.
  Flexible system administration.
  Management and distribution of the flow of transactions.
  Sending and receiving of messages between client and server applications.
  Interfacing with data entry systems to create and manage interactive data entry forms.
  Dealing with resource managers, such as data base management systems (DBMSs) using standardized interfaces.

Enterprise Computing in a New Age (called Encina) is a product based on technologies from the X/Open Consortium and Open Software Foundation’s DCE. It is a product of Transarc Corp. and provides a highly reliable and easy-to-use transaction-processing environment for open systems and client/server environments. It supports all the core functionality described above using components of DCE with some of its own extensions for multithreading. Encina can start and stop servers dynamically and supports user-defined and abstract data types. Hardware vendors usually remarket this product.

Tuxedo, from the former UNIX System Laboratories, requires that application resource managers running under Tuxedo adhere to standard interfaces, namely the X/Open XA interface. The XA interface is a component of the distributed transaction processing (DTP) reference model. XA-compatible interfaces are built into all major UNIX DBMS products. An additional advantage of Tuxedo is that it is independent of underlying network technologies through its use of the UNIX System V Transport Layer Interface (TL1), which supports NetBIOS, Advanced Program-to-Program Communications Logical Unit 6.2 (APPC/LU6.2), Open Systems Interconnection (OSI) protocols, and TCP/IP. Tuxedo is also usually remarketed by the hardware vendors.

TOP END from AT&T is also based on X/OPEN’s DTP environment and uses XA interfaces to UNIX DBMSs. It has direct support for INIX TL1, APPC/LU6.2, and OSI and advanced administration capabilities. It differs from Tuxedo in its support of Kerberos (a crytography-based computer and network security technology) and its ability to dynamic load-leveling.

SQL Access Group has merged with X/Open’s Data Management Working Group in the new X/Open SQL Access Group. Work is expected to be done on SQL, Stored Procedures,a nd the SQL Call Level Interface. This work should further synthesize standardized messaging protocols.

Styles of Client/Server Computing

The Gartner Group Mode

The Gartner Group model of client of client/server computing is perhaps one of the more widely used. As shown in Exhibit 6-3-10, reading from left to right, the model goes from distributed presentation to distributed data management. Above the network line are the capabilities resident in the server software, and below the network line are the capabilities resident in the client software.


Exhibit 6-3-10.  Gartner Group Model of Client/Server Computing

Each variation carries its own impact on application segmentation between the client a nd the server:

  Distributed presentation. All the application logic and data management are resident in the server. The presentation is segmented between the client and the server and is more along hardware than software lines as computer terminals are used for the distributed part of the presentation layer. This is really little change from the monolithic model. Its only advantage is in the low-cost desktop hardware.
  Remote presentation. Shared applications are run on optimized platforms, placing some of the capability closer to the user. With remote presentation, the client application contains all the presentation logic. The client application can usually run on low-cost PCs or X-terminals. The presentation may or may not use a windowed environment. One windowed environment, X-windows, is itself an example of remote presentation.
  Distributed logic. Application logic can be segmented in an optimal fashion such that the most efficient platform is used for execution. This is where “the network is the computer” can happen. Application segmentation occurs such that it may be spread across two or more platforms. Done correctly, it also allows for redistribution of application logic over time. In this scenario, resource optimization can occur. The stored procedures of Oracle7 are a good example of distributed functions. All the logic of the procedures can be on the server or shared between the server applications and the client applications.
  Remote data access. In this variation, all the application logic is in the client software and all the data management is in the server software. This is the most common form of client/server and accounts for approximately 80% of all client/server implementations. Data management is a shared responsibility between the client and the server.
  Distributed data management. In this variation, the data base is distributed between the client and the server. All functionality besides data management is the purview of the client and hence most activity occurs there.


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