Whenever a member is deleted, the space it occupied is unusable for storing other data.

Likewise, if a member is re-written, it is stored in a new spot at the back of the PDS and leaves wasted “dead” space in the middle.

They are most often used for storing multiple JCL files, utility control statements and executable modules.

updating typed datasets-59

This type of data set is often used to hold executable programs (load modules), source program libraries (especially Assembler macro definitions), and Job Control Language.

A PDS may be compared to a Zip file or COM Structured Storage.

Regardless of organization, the physical structure of each record is essentially the same, and is uniform throughout the data set.

This is specified in the DCB , means a logical record could be spanned across two or more blocks, with flags in the RDW indicating whether a record segment is continued into the next block and/or was continued from the previous one.

Programmers utilize various access methods (such as QSAM or VSAM) in programs for reading and writing data sets.

Access method depends on the given data set organization.It can have tables, rows, constraints and relationships between tables.Though the dataset is capable of handling relational data efficiently, it fails if you try to extend its capabilities.Before looking at extending the capabilities of the .NET 2.0 dataset with business functionality, it is important to look at typed datasets.The dataset is an integral part of Microsoft’s new data access model ADO. It introduces a simple offline method for retrieving and updating data.