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Chapter 11: Transaction managers on z/OS CICS and IMS

Chapter 11: Transaction managers on z/OS CICS and IMS. Chapter objectives. Be able to: Describe the role of large systems in a typical online business . List the attributes common to most transactional systems. Explain the role of CICS in online transaction processing

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Chapter 11: Transaction managers on z/OS CICS and IMS

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  1. Chapter 11: Transaction managers on z/OS CICS and IMS

  2. Chapter objectives • Be able to: • Describe the role of large systems in a typical online business. • List the attributes common to most transactional systems. • Explain the role of CICS in online transaction processing • Describe CICS programs, CICS transactions, and CICS tasks • Explain what conversational and pseudo-conversational programming is • Explain CICS and Web-enabling • Discuss the IMS components

  3. Key terms in this chapter task/thread region PSB IMS TM transaction unit of work two-phase commit wireless access point (WAP) • BMP • BMS • conversational • CICS TS • CICS command • IRLM • multithreading • multitasking

  4. CSMG

  5. Example of online processing: a travel agency • Mainframe applications designed for: • employee and customer information • contacts with car rental companies • hotels • airline schedules • theaters • Changes must be immediately reflected to end-users • Contrast with batch processing

  6. Example of online processing (continued)

  7. A practical example

  8. Transactional systems • Requirements: ACID Properties • Atomicity • Consistency • Isolation • Durability

  9. Transactional systems: terminology • Commit and roll back • Multitasking • Multithreading • Thread • Reentrancy

  10. Characteristics of a transactional systems

  11. Two-phase commit - First commit then 2 phase commit

  12. What is CICS? • Customer Information Control System • Transactional subsystem of z/OS which: • runs online applications • At the same time, many users, same application(s) • manages the sharing of resources • integrity of data • prioritization of execution, with fast response.

  13. CICS in a z/OS system

  14. Languages & Platforms • Languages: • COBOL • OO COBOL • C • C++ • JAVA (JCICS) • PL/I • Assembler • Platforms: • zSeries (z/OS, OS/390, VSE) • Intel servers • TXSeries (AIX, HP-UX, Solaris and Windows)

  15. Source TSO Submit Translator Translate Translated Program Compiler Compile Object Module Link Edit Bind Load Module //DFHRPL DD DSN=CICSV3.SDFHLOAD1,DISP=SHR // DD DSN=CICSV3.SDFHLOAD2,DISP=SHR // DD DSN=CICSV3.ULOADLIB,DISP=SHR Program Library Generating a CICS Application Program Example: COBOL 1) 2) 3)

  16. CICS Programming road-map • Design application • Write & test program (includes compiling) • Define program & transaction in CICS resources • Define other resources (files, queues, etc…) in CICS resources • Make resources known to CICS

  17. LPAR A LPAR B * A CICS subsystem may be composed of one or more address spaces to isolate functionality, administration and throughput. As an example: - TOR = Terminal Owning Region - AOR = Application Owning Region - FOR = File Owning Region - WOR = Web Owning Region - ROR = Routing Owning region * This is a configuration known as: Multi Region Operation (MRO) LPAR C AOR TOR CICS FOR Other Subsyst AOR Other Subsyst CICS WOR Other Subsyst AOR CICS CICS Terminals Programs Files Configuration } one address space containing all functions TCT SYS 2 PPT FCT Other Subsyst PCT CICS CICS CICS ROR * CICS has strong flexibility for business configuration needs thru table definitions CICS Other Subsyst CICS Inter-System Communication (ISC) Other Subsyst CICS in one or multiple LPARS SYS 1

  18. CICS CICS CICS CICS Features • Transaction (Message) Driven • Multitasking • Multithreading • Quasi-reentrant

  19. CICS Programs, Transactions, Tasks and Tables Transaction > Program Control Table (PCT)- Maps input transaction to Application >Program Processing Table (PPT) – Contains names of application programs Files >File Control Table (FCT) – User Files names e.g. where to save user state >Terminal Control Table (TCT) - terminals, sequential devices, logical units, and other systems to CICS Table Definitions are usually done by the CICS Systems Programmer through a CICS facility called Resource Definition On-Line (RDO). Configuration TCT PPT FCT PCT ****

  20. A CICS Transaction A transaction is given a 4-character name in the program control table (PCT) A transaction is one or more application programsthat do the processing needed. You describe each transaction type to CICS with a transaction resource definition. It gives the type a name (TRANSID) and tells CICS about the work to be done, such as what program to invoke first A unit of Work is a complete operation that is recoverable; can be committed or backed out entirely In many cases, a CICS transaction is unit of work. When CICS receives a request, it starts a new task associated with this instance of the transaction, with a particular set of data, on behalf of a user at a terminal. It is analogous to a thread. When the transaction completes, the task is terminated.

  21. A CICS Transaction You can see how these two sets of definitions, transaction and program, work in concert: >The user types in a transaction identifier at the terminal (or the previous transaction determined it). > CICS looks up this identifier in the list of installed transaction definitions. This tells CICS which program to invoke first. > CICS looks up this program in the list of installed transaction definitions, finds where it is, and loads it (if not already loaded). > CICS builds the control blocks necessary for this combination of transaction and terminal, using both sets of definitions. > CICS passes control to the program, which begins running. This program may pass control to any other program in the installed program definitions, in the course of completing the transaction.

  22. Conversational and Pseudo Conversational Transaction A conversational transaction is when the programs being executed exists while a user interacts with it. A non-conversational transaction processes one input, responds, and ends. It never pauses to read a second input from the terminal. In CICS pseudo-conversational processing, in which a series of non-conversational transactions gives the appearance (to the user) of a single conversational transaction. -No transaction exists while the user inputs information to the screen; -CICS reads the input when the user gets around to sending it. (next slide) Note: TPF runs in this mode

  23. A Task executing in Multi-Tasking • Task Control • Application Program(s) • Basic Mapping Support • File Control • Program Control • Temporary Storage Control • Transient Data Control • Journal Control (logging) • Trace Control • Dump Control • Interval Control • Storage Control

  24. Conversational  Pseudo-Conversational

  25. Program Control There are two CICS commands for passing control from one program to another. >One is the LINK command, which is similar to a CALL statement. > The other is the XCTL (transfer control) command. When one program LINKs another, the first program stays in main storage. When the second (linked-to) program returns, the first program resumes after the LINK. In contrast, when one program XCTLs to another, >the first program is considered terminated, and >the second operates at the same level as the first. When the second program returns, control is returned not to the first program, but to the last program that issued a LINK.

  26. Program Control RETURN XCTL LINK LOAD RELEASE EXEC CICS LINK PROGRAM(PROGRAM-2) END_EXEC. EXEC CICS XCTL PROGRAM(PROGRAM-3) END_EXEC.

  27. CICS COMMUNICATION AREA (COMMAREA) This area of a program is used to pass information between other programs and transactions. • It is automatically provided to you via the Translator phase • It initially provides you one byte to be used as a programming SW although it can range up to 32K bytes in size .

  28. CICS and Web-enabling • 4 major elements of web-enabled applications: • Presentation logic • Integration logic • Business logic • Data logic

  29. CICS Transaction Gateway and WebSphere Application Server

  30. What is IMS? • Information Management System • 3 components: • The Transaction Manager (TM) • the Database Manager (DB) • Set of system services, providing common services to the TM and DB

  31. IMS overview

  32. IMS Transaction Manager (TM) messages • Four types of messages: • Transactions • To go to another logical destination • Commands for IMS • For the IMS APPC feature to process

  33. Summary : Transaction based systems • Interaction with the computer happens online through the help of a transaction manager. • The continued growth of the Internet has caused many corporations to consider the best ways to make their legacy systems available to users on the Internet. • CICS is a transactional processing subsystem. CICS applications are traditionally run by submitting a transaction request. • Information Management System (IMS) consists of three components: • Transaction Manager (TM) • Database Manager (DB) • A set of system services common to both TM and DB

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