Overview of the syntax for DDM terms supported by IMS

IMS supports the general syntax of terms defined by the distributed data management (DDM) architecture.

All DDM commands, reply messages, and chained objects begin with a 6-byte data stream structure header (DSSHDR), followed in order by a 2-byte binary integer that defines the length of the term (LL), and a 2-byte hexadecimal codepoint (CP) that uniquely identifies the DDM term, and data, if any.

Parameters of commands, messages, and objects start with LL, followed in order by CP and the data. Parameters, which are also known as instance variables, do not include a DSSHDR.

Some data structures, such as the IMS product-unique data structures aibStream, dbpcbStream, and iopcbStream, do not include DSSHDR, LL, or CP.