IMS DB DL/I Processing IMS/DB

What is IMS DB DL/I Processing?

IMS DB stores data at different levels. Data is retrieved and inserted by issuing DL/I calls from an application program. We will discuss about DL/I calls in detail in the upcoming chapters. Data can be processed in the following two ways:

  • Sequential Processing
  • Random Processing
  • Sequential Processing

When segments are retrieved sequentially from the database, DL/I follows a predefined pattern. Let us understand the sequential processing of IMS DB.

sequential_processing  (1)

listed below are the factors to be aware of sequential processing:

  • The predefined sample for getting access to records in DL/I is first down the hierarchy, then left to right.
  • the root segment is retrieved first, then DL/I movements to the first left child and it goes down till the lowest level. At the lowest level, it retrieves all of the occurrences of twin segments. Then it goes to the proper phase.
  • To understand higher, observe the arrows in the above figure that show the glide for accessing the segments. The library is the root segment and the flow begins from there and goes to cars to access a single file. The same process is repeated for all occurrences to get all the facts statistics.
  • Whilst accessing data, this system makes use of the location inside the database which enables to retrieve and insert segments.

Random Processing

Random processing is also known as direct processing of data in IMS DB. Let us take an example to understand random processing in IMS DB:

random_processing

listed under are the factors to observe about random processing:

  • segment occurrence that needs to be retrieved randomly calls for key fields of all of the segments it depends upon. those key fields are supplied by using the application software.
  • A concatenated key absolutely identifies the direction from the basis segment to the segment which you need to retrieve.
  • think you need to retrieve an occurrence of the commerce segment, then you definitely want to supply the concatenated key field values of the segments it depends upon, such as Library, Books, and commerce.
  • Random processing is quicker than sequential processing. In real-global state of affairs, the packages integrate both sequential and random processing strategies collectively to acquire best results.

Key field

  • points to note:
  • A key discipline is likewise called a sequence field.
  • A key subject is present inside a phase and it is used to retrieve the phase prevalence.
  • A key area manages the phase prevalence in ascending order.
  • In every section, only a single field can be used as a key subject or sequence area.

Search field

As mentioned, simplest a single field can be used as a key subject. in case you want to search for the contents of other phase fields which are not key fields, then the sector that is used to retrieve the information is referred to as a search field.

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