29-05-2012, 03:13 PM
Infosys Technologies Limited
Infosys Technologies Limited.pdf (Size: 365.26 KB / Downloads: 48)
Introduction
DB2 Is a Relational DBMS developed by IBM for computers running under MVS,
its most advanced operating system for large computers. DB2 supports SQL
(structured query language), which has been standardized by ANSI (American National
Standards Institutes) and ISO (International Standards Organization) and has become
the standard for all relational DBMSs.
DB2 co-operates with attaches to is the technical term-any of three MVS subsystems
environments : IMS, CICS, and TSO. These subsystems cooperate with DB2 facilities
to provide such services as data communications and control of transactions, which are
group of database operations that must be coordinated to avoid the introduction of errors.
CICS is a teleprocessing monitor, a program for controlling online transactions those
that execute as they are entered from a terminal allowing users to interact with the
computer. IMS/DB/DC is a well established nonrelational DBMS, which includes a
teleprocessing monitor. TSO also contains a teleprocessing monitor that can be used by
DB2. DB2 applications running under TSO may be online or batch.
CICS attachment facility ADB2 subcomponent that uses the MVS subsystem
interface (SSI) and cross storage linkage to process requests from CICS to DB2 and to
coordinate resource commitment.
IMS attachment facility A DB2 subcomponent that uses MVS subsystem interface
(SSI) protocols and cross-memory linkage to process requests from IMS to DB2 and to
coordinate resource commitment.
TSO attachment facility A DB2 facility consisting of the DSN command processor
and DB21. Applications that are not written for the CICS or IMS environments can
run under the TSO attachment facility.
Database Request Module
The precompiler output include a database request module (DBRM) which contains
SQL statements extracted from the source program. The SQL statements in a DBRM
are those executable statements that must be bound before they can be executed. The
DBRM is kept as a member of a partitioned data set (library) and is given the name of
the program. It also contains a consistency token to distinguish it from other DBRMs
derived from other versions of the program.
The Bind Process
The bind process establishes a relationship between an application program and its
relational data. This step is necessary before you can execute your program. Currently,
DB2 allows you two basic ways of binding a program : to a package, or directly to an
application plan. If your application is to make use of remote units of work, then you
must use packages.
DB2 Objects
A DB2 object is something that can be defined using an SQL CREATE statement The
objects are classified as follows :
Tables Indexes
Views
Table spaces
Storage groups
Data bases
Synonyms
Aliases
The Catalog
Each DB2 maintains a set of tables containing information about the data it manages.
These tables are collectively known as the catalog. The catalog tables contain
information about DB2 objects such as tables, views, and indexes.
With appropriate authorization, you can retrieve data from catalog tables by using SQL
statements, just as you would with any other table. Each DB2 ensures that at all times
its catalog contains accurate descriptions of the objects that the DB2 controls.
Unit of work
A unit of work is a logically distinct procedure containing one or more steps that change
one or more pieces of data. If all the steps complete successfully, you want the data
changes made to become permanent. But, if any of the steps fail to complete
successfully, you want all modified data to be returned to the value before the procedure
began.
For example, suppose two employees in the sample table DSN8230.EMP exchange
offices. Their office phone numbers need to be exchanged in the PHONENO column.