21⟩ What is meant by MPP mode?
► True Online processing.
► Transaction are entered at terminal and stored in message queue.
► Databases accessed must be offline.
IMS DB
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“IBM Information Management System (IMS) is a joint hierarchical database and information management system with extensive transaction processing capabilities.”
39 IMS DB Questions And Answers
22⟩ What is meant by Batch DL/I mode?
► True Batch processing.
► No data communication services are used.
► Databases accessed must be offline.
23⟩ What are the processing modes available in IMS DB?
► Batch DL/I
► MPP Mode - (Message Processing Program)
► BMP Mode - (Batch Message Processing)
24⟩ What is the disadvantage of dynamic generation of ACB?
Everytime the program is run., the ACB needs to be built.
25⟩ What is the advantage of dynamic generation of ACB?
It can be made sure that the ACB generated incorporates all the latest changes to the PSB and DBD.
26⟩ Explain PSBGEN process?
PSBGEN control statements consists of Assembler Language macro statements. The macros are supplied by IBM in a library named IMSVS.MACLIB. That invokes a cataloged procedure usually called PSBGEN and stored in PSBLIB. Each PSB consists of one or more control blocks called Program Control Block (PCB). Each PCB within a PSB defines one logical structure. All the PCBs within a PSB are collectively knows as an Application Data Structure.
IMS allows a PSB to define more than one logical data structure because a program is allowed to access to more than one database. A program us also allowed to concurrently access different parts of the same database. IMS allows the DBA to define any number of logical data structure in a single PSB.
27⟩ Explain ACBGEN process?
ACB is a consolidation of PSB and DBD information.
► For online programs
ACBs must be prebuilt using the ACBGEN utility i.e., ACBGEN must be run which will merge DBD and PSB and generate ACB.
► For batch programs
ACBs can be generated either at execution time (dynamically using IMS.DBDLIB and IMS.PSBLIB as input (PARM=DL/I)) or ahead of time (prebuilt ACB from IMS.ACBLIB can be used (PARM=DBB)).
28⟩ What is the advantage of creating the ACBs well ahead of time?
► Application program's scheduling consumes less time
► Less storage
29⟩ What are the two types of fields available in IMS DB?
Key Fields - (PROCOPT=K)
► Used to sequence the database and can't be changed
► It’s the field within a segment, used to identify the occurrence of the segment
► used to maintain the IMS segments in ascending sequence.
Search Fields - (PROCOPT=G)
► Used to search for a segment, without the segment being sequenced on that field
► A segment need not have a key or search field.
Both types of fields can be used to search the database.
30⟩ What is ACB?
Application Control Block is an internal control block consisting of combined information from the DBD and PSB.
31⟩ Explain DBDGEN process?
DBDGEN control statements consists of Assembler Language macro statements. The macros are supplied by IBM in a library named IMSVS.MACLIB. DBDGEN control statements are normally coded by the DBA and submitted to the system with JCL. That invokes a cataloged procedure usually called DBDGEN. The DBDGEN procedure causes the DBDGEN control statements to the processed by the assembler producing the object module. The object module is then passed to the linkage editor which, in turn, stores a load module in another IMS Library called as IMS.DBDLIB or IMSVS.DBDLIB.
The DBD process is normally preformed only once for a database. All applications use the DBD in accessing the information on the database. A new DBD is normally created only if the physical nature of the database changes.
32⟩ What information does a DBD contain?
DBD information includes:
► Database name, Access method
► Dataset name
► Segment name, length, parent
► Key field name, length, location, type
► Search field name, length, location, type
33⟩ What is a segment in IMS?
Segment is the smallest unit of information that IMS transfers to and from database. Segment may contain one or more fields.
34⟩ What is PCB?
Program Communication Block defines which database the program will access and the type of access allowed. It is defines the programmer's view of the database.
35⟩ What is PSB?
Program Specification Block defines the programs view of the database and application programs access authority to database. It defines the logical data structure. A PSB is made up of one or more PCBs (Program communication blocks).
36⟩ Which languages does IMS support / application program languages?
COBOL, PL/1, C, VS Pascal, REXX, Ada and Assembler.
37⟩ What are the main control blocks available in IMS DB?
There are three control blocks (also known as DL/I control blocks)
► Database Description (DBD)
► Program Specification Block (PSB)
► Application Control Block (ACB)
38⟩ What is DBD?
DBD (Database Definition) is used to define the physical structure of the database.
► One DBD for each database
► Created by a series of control statements - by a process called DBDGEN
► Used by DL/I whenever database is used
39⟩ What information does a PSB contain?
PSB information includes:
► PCB - defines the database to be accessed by the application program.
► SENSEG - defines the segment types to which the application program will be sensitive.
► SENFLD - defines the fields in the segment type to which the application program will be sensitive.
► PROCOPT - defines the types of access to the database or segment.
