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Custom programs can access VSAM datasets through Data Definition (DD) statements in Job Control Language (JCL), via dynamic allocation or in online regions such as in Customer Information Control System (CICS). Both IMS/DB [citation needed] and Db2 [2]: 41 [6] are implemented on top of VSAM and use its underlying data structures.
IBM categorizes some of these programs as utilities [1] [a] and others as service aids; [2] the boundaries are not always consistent or obvious. Many, but not all, of these programs match the types in utility software. The following lists describe programs associated with OS/360 and successors. No DOS, TPF or VM utilities are included.
Job Control Language (JCL) is a scripting language used on IBM mainframe operating systems to instruct the system on how to run a batch job or start a subsystem. [1] The purpose of JCL is to say which programs to run, using which files or devices [2] for input or output, and at times to also indicate under what conditions to skip a step.
JCL is used to define jobs to both JES2 and JES3, but small changes usually need to be made to the JCL to get a job written for one JES to run on the other. A common issue was that JES3 checked that all datasets listed in the JCL existed before execution or that there was a prior step where the dataset was defined as NEW,CATLG.
Apache Commons Logging (previously known as Jakarta Commons Logging or JCL) is a Java-based logging utility and a programming model for logging and for other toolkits. It provides APIs , log implementations, and wrapper implementations over some other tools.
An entry-sequenced data set (ESDS) is a type of data set used by IBM's VSAM computer data storage system. [1]: 5 Records are accessed based on their sequential order, that is, the order in which they were written to the file; which means that accessing a particular record involves searching all the records sequentially until it is located, or by using a relative physical address (Relative byte ...
[2]: p.106 Relative track addresses are three byte fields in the form TTR. All subfields are binary numbers. TT is the relative track number in the file, starting with zero. R is the record number on the track. Relative block numbers are four byte (fullword) binary numbers indicating the block number in the file. The first block is block 0.
By design, programs written for MVS run on z/OS without modification. At first IBM described MVS as simply a new release of OS/VS2 , but it is, in fact a major rewrite. OS/VS2 release 1 is an upgrade of OS/360 MVT that retained most of the original code and, like MVT, is mainly written in assembly language .