Job stream

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In a non-interactive computer system, particularly IBM mainframes, a job stream, jobstream, or simply job is the sequence of job control language statements (JCL) and data (called instream data) that comprise a single "unit of work for an operating system". [1] The term job traditionally means a one-off piece of work, and is contrasted with a batch (executing the same steps over many inputs), but non-interactive computation has come to be called "batch processing", and thus a unit of batch processing is often called a job, or by the oxymoronic term batch job; see job for details. Performing a job consists of executing one or more programs. Each program execution, called a job step, jobstep, or step, is usually related in some way to the others in the job. Steps in a job are executed sequentially, possibly depending on the results of previous steps, particularly in batch processing.

IBM American multinational technology and consulting corporation

International Business Machines Corporation (IBM) is an American multinational information technology company headquartered in Armonk, New York, with operations in over 170 countries. The company began in 1911, founded in Endicott, New York, as the Computing-Tabulating-Recording Company (CTR) and was renamed "International Business Machines" in 1924.

In computing, a job is a unit of work or unit of execution. A component of a job is called a task or a step. As a unit of execution, a job may be concretely identified with a single process, which may in turn have subprocesses which perform the tasks or steps that comprise the work of the job; or with a process group; or with an abstract reference to a process or process group, as in Unix job control.

Computerized batch processing, since the 1964 introduction of the IBM System/360, has primarily referred to the scripted running of one or more programs, as directed by Job Control Language, with no human interaction other than, if JCL-requested, the mounting of one or more pre-determined input and/or output computer tapes.

Contents

The term "job stream" is particularly associated with mainframes; in the IBM z/OS operating system, a job is initiated by a // JOB and terminated by the next // JOB or // statement. Each job step consists of one // EXEC statement indicating the program to be executed and usually multiple // DD statements defining the files and devices to be used.

z/OS 64-bit operating system for IBM mainframes

z/OS is a 64-bit operating system for IBM mainframes, produced by IBM. It derives from and is the successor to OS/390, which in turn followed a string of MVS versions. Like OS/390, z/OS combines a number of formerly separate, related products, some of which are still optional. z/OS offers the attributes of modern operating systems but also retains much of the functionality originating in the 1960s and each subsequent decade that is still found in daily use. z/OS was first introduced in October 2000.

A computer file is a computer resource for recording data discretely in a computer storage device. Just as words can be written to paper, so can information be written to a computer file. Files can be edited and transferred through the internet.

Example

A simple example of a job stream is a system to print payroll checks which might consist of the following steps, performed on a batch of inputs:

  1. Read a file of data containing employee id numbers and hours worked for the current pay period (batch of input data). Validate the data to check that the employee numbers are valid and that the hours worked are reasonable.
  2. Compute salary and deductions for the current pay period based on hours input and pay rate and deductions from the employee's master record. Update the employee master "year-to-date" figures and create a file of records containing information to be used in the following steps.
  3. Print payroll checks using the data created in the previous step.
  4. Update bank account balance to reflect check numbers and amounts written.

Each step depends on successful completion of the previous step. For example, if incorrect data is input to the first step the job might terminate without executing the subsequent steps to allow the payroll department to correct the data and rerun the edit. If there are no errors the job will run to completion with no manual intervention.

See also

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References

  1. ↑ IBM Corporation. "Glossary of z/OS terms and abbreviations - job" . Retrieved February 18, 2013.
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