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On OS/360 and derived mainframe systems, most programs never specify files (usually called datasets) directly, but instead reference them indirectly through the Job Control Language (JCL) statements that invoke the programs. These data definition (or "DD") statements can include a "disposition" (DISP=...
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.
This data set comparison is performed at the logical record level. Therefore, IEBCOMPR is commonly used to verify that a backup copy of a data set is correct (exact match to the original). During processing, IEBCOMPR compares each record from each data set, one by one.
A partitioned data set (PDS) [7] is a data set containing multiple members, each of which holds a separate sub-data set, similar to a directory in other types of file systems. This type of data set is often used to hold load modules (old format bound executable programs), source program libraries (especially Assembler macro definitions), ISPF ...
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.
^ ASN.1 has X.681 (Information Object System), X.682 (Constraints), and X.683 (Parameterization) that allow for the precise specification of open types where the types of values can be identified by integers, by OIDs, etc. OIDs are a standard format for globally unique identifiers, as well as a standard notation ("absolute reference") for ...
Many of the constants and variables contained within a DCB may be left blank (i.e., these default to zero). The OPEN process results in a merge of the constants and variables specified in the DD JCL statement, and the dataset label for existing magnetic tape and direct-access datasets, into the DCB, replacing the zero values with actual, non-zero values.
Modern versions of MVS (e.g., z/OS) use datasets as containers for Unix filesystems along with facilities for partially integrating them. That is, Unix programs using fopen() can access an MVS dataset and a user can allocate a Unix file as though it were a dataset, with some [NB 5] restrictions.