DATA DICTIONARY .

DATA DICTIONARY .

Type of a table or structure                                                

                                                                           

    The table type determines how the logical table description defined in 

    the ABAP/4 Dictionary is reproduced on the database.                   

                                                                           

    There are the following table types:                                   

    o  transparent table                                                   

    o  structure                                                           

    o  append structure                                                    

                                                                           

    For internal purposes, such as storing control data or update texts,   

    there are in addition the following table types:                       

    o  pooled table                                                        

    o  cluster table                                                        

    o  generated view structure                                            

                                                                           

 Transparent table                                                             

                                                                              

     There is a physical table on the database for each transparent table. The

     names of the physical tables and the logical table definition in the     

     ABAP/4 Dictionary correspond.                                            

     All business data and application data are stored in transparent tables. 

                                                                              

 Structure                                                                       

                                                                                

     No data records exist in the database for a structure. Structures are      

     used for the interface definition between programs or between screens and  

     programs.                                                                  

                                                                                

 Append structure                                                               

                                                                               

     An append structure defines a set of fields which belong to another table 

     or structure but which are treated in the correction administration as    

     its own object.                                                           

     Append structures are used to support modifications.                      

                                                                                

 Pooled table                                                                

                                                                             

     Pooled tables can be used to store control data (e.g. screen sequences, 

     program parameters or temporary data). Several pooled tables can be     

     combined to form a table pool. The table pool corresponds to a physical 

     table on the database in which all the records of the allocated pooled  

     tables are stored.                                                       

                                                                             

 Cluster table                                                                  

                                                                                 

     Cluster tables contain continuous text, for example, documentation.        

     Several cluster tables can be combined to form a table cluster. Several    

     logical lines of different tables are combined to form a physical record   

     in this table type. This permits object-by-object storage or               

     object-by-object access. In order to combine tables in clusters, at least  

     parts of the keys must agree. Several cluster tables are stored in one     

     corresponding table on the database.                                       

                                                                               

 Generated view structure                                                        

                                                                               

     In activation a structure is generated for a view. This structure serves  

     as interface for the runtime environment. It does not generally appear in 

     the ABAP/4 Dictionary.                                      

What is a Data Class?

    The Data class determines in which tablespace the table is stored when it

    is created in the database.

What is a Size Category?

    The Size category describes the probable space requirement of the table

    in the database.

How Many types of size categories and data classes are there?

    There are five size categories (0-4) and 11 data classes, only three of

    which  are appropriate for application tables:

            - APPL0 - Master data (data frequently accessed but rarely updated)

            - APPL1 - Transaction data (data that is changed frequnetly)

            - APPL2 - Organisational data (customizing data that is entered when system is

                                                            configured and then rarely changed)

 What are control tables?

    The values specified for the size category and data class are mapped to

    database-specific values via control tables.

 What is the function of the transport system and workbench organiser?

    The function of the transport system and the Workbench Organizer is to

    manage any changes made to objects of the ABAP/4 Development Workbench

    and to transport these changes between different SAP systems.

 What is a table pool?

    A table pool (or pool) is used to combine several logical tables in the

    ABAP/4 Dictionary. The definition of a pool consists of at least two key

    fields and a long argument field (VARDATA).

 What are pooled tables?

    These are logical tables which must be assigned to a table pool when they

    are defined. Pooled tables can be used to store control data (such as

    screen sequences or program parameters).

  What is a table cluster?

     A table cluster combines several logical tables in the ABAP/4 Dictionary.

     Several logical rows from different cluster tables are brought together

     in a single physical record. The records from the cluster tables

     assigned to a cluster are thus stored in a single common table in the

     database.

 Which objects are independent transport objects?

      Domains, Data elements, Tables, Technical settings for tables,

      Secondary indexes for transparent tables,  Structures, Views,

      Matchcode objects, Matchcode IDs, Lock objects.

What are the Data types of the external layer?

ACCP, CHAR, CLNT, CUKY,CURR, DATS, DEC, FLTP, INT1,INT2, INT4, LANG, LCHR,LRAW, NUMC, PREC, QUAN,RAW ,TIMS, UNIT, VARC.

 What are the Data types of the ABAP/4 layer?

      Possible ABAP/4 data types:

      C: Character.

      D: Date, format YYYYMMDD.

      F: Floating-point number in DOUBLE PRECISION (8 bytes).

      I: Integer.

      N: Numerical character string of arbitrary length.

      P: Amount or counter field (packed; implementation depends on hardware

          platform).

      S: Time stamp YYYYMMDDHHMMSS.

      T: Time of day HHMMSS.

      V: Character string of variable length, length is given in the first

         two bytes.

      X: Hexadecimal (binary) storage.

How can we set the tablespaces and extent sizes ?

You can specify the extent sizes and the tablespace (physical storage

        area in the database) in which a transparent table is to be stored by

        setting the size category and data class.

What is a data dictionary ?

Data dictionary is a central source of data in a data management system. Its main function is to support the .It has details about

            - What data is contained ?

            - What are the attributes of the data ?

            - What is the relationship existing between the various data elements ?

What functions does a data dictionary perform ?

       In a  data management system, the principal functions performed by the  data dictionary are

            - Management of data definitions

            - Provision of information for evaluation

            - Support for software development

            - Support for documentation

            - Ensuring that the data definitions are flexible and up-to-date.

A field containing currency amounts (data type CURR)  must be assigned to a reference table and a reference field. Explain.

As a reference table, a system table containing all the valid currencies is assigned or any other table which contains a field with the currency key format. This field is called as reference field.

The assignment of the field containing currency amounts to the reference field is made at runtime.  The value in the reference field determines the currency of the amount.

What is the significance of Technical settings (specified while creating a table in the data dictionary) ?

By specifying technical settings we can control how database tables are created in the database.

The technical settings allows us to

            - optimize storage space requiremnets

            - table access behaviour

            - buffering required

            - changes to entries logged

What is the significance of Delivery Class ?

- The delivery class controls the degree to which the SAP or the customer is    responsible  for table maintenance

            - whether SAP provides the table with or without contents.

            - determines the table type.

-  determines how the table behaves when it is first installed, at upgrade, when it is transported, and when a client copy is performed.

What is the maximum number of structures that can be included in a table or structure

            - Nine.

What are the two methods of modifying Sap standard tables ?

            - Append Structures and

            - Customizing Includes.

What is the difference between a Substructure and an Append Structure ?

- In case of a substructure, the reference originates in the table itself, in the forma of a statement .include... .

-          In case of an append structure, the table itself remains unchanged and the refrence originates in the append structure.

What are the two ways for restricting the value range for a domain ?

            - By specifying fixed values.

            - By stipulating a value table.

What is a Match Code ?

 Match Code is a tool to help us to search for data records in the system. Match codes are an efficient and user-friendly search aid where key of  a record is unknown.

What are the two levels in defining a Match Code ?

            - Match Code object

            - Match Code Id.

What is the maximum number of match code Id's that can be defined for one Match code object ?

            - 36. A match code Id is a one character ID which can be a letter or a number.

Can we define our own Match Code ID's for SAP Matchcodes ?

Yes, the numbers 0 to 9 are reserved for us to create our own Match Code IDs for a SAP defined Matchcode object.

What is an Update type with reference to a Match code ID?

If the data in one of the base tables of a matchcode ID changes, the matchcode data has to be updated. The update type stipulates when the matchcode is to be updated and how it is to be done. The update type also specifies which method is to be used for Building matchcodes . You must specify the update type when you define a matchcode ID.

What are conversion routines ?

-          Non standard conversions from display format to sap internal format and vice-versa are implemented with so called conversion routines.

Aggregated Objects

Views, matchcodes, and lock objects are also called aggregate objects because they are formed from several related tables.

What is a View ?

- A view is a logical view on one or more tables. A view on one or more tables i.e, the data from a view is not actually physically stored instead being derived from one or more tables. A view can be used to summarize data which is distributed among several tables

How many types of Views are there ?

-          Database View   (SE11)

Database views are implement an inner join, that is, only records of the primary table (selected via the join operation) for which the corresponding records of the secondary tables also exist are fetched. Inconsistencies between primary and secondary table could, therefore, lead to a reduced selection set.

In database views, the join conditions can be formulated using equality relationships between any base fields. In the other types of view, they must be taken from existing foreign keys. That is, tables can only be collected in a maintenance or help view if they are linked to one another via foreign keys.

-          Help View    ( SE54)

Help views are used to output additional information when the online help system is called.

When the F4 button is pressed for a screen field, a check is first made on whether a matchcode is defined for this field. If this is not the case, the help view is displayed in which the check table of the field is the primary table. Thus, for each table no more than one help view can be created, that is, a table can only be primary table in at most one help view.

-          Projection View

Projection views are used to suppress or mask certain fields in a table (projection), thus minimizing the number of interfaces. This means that only the data that is actually required is exchanged when the database is accessed.

A projection view can draw upon only one table. Selection conditions cannot be specified for projection views.

-          Maintenance View   ( SE54 )

      Maintenance views enable a business-oriented approach to looking at data, while at   

      the same time, making it possible to maintain the data involved. Data from several 

      tables can be summarized in a maintenance view and maintained collectively via this

      view. That is, the data is entered via the view and then distributed to the underlying

      tables by the system.

What is Locking ?

-          When two users simultaneously attempt to access the same data record, this is synchronised by a lock mechanism.

When dialog transactions are programmed, locks are set and released by calling certain function modules. These function modules are generated automatically from the definition of so-called lock objects in the ABAP/4 Dictionary.

To synchronize the access to a table by setting and removing locks, a Lock object has to be defined in the ABAP/4 Dictionary. Activating the lock object automatically creates function modules for setting and removing locks. These function modules must be included when programming interactive transactions.

Lock Mechanism :

To set locks, a lock object must be defined in the ABAP/4 Dictionary. In this lock object, those tables in which data records are to be locked by calling a lock are determined. All tables included in a lock object must be connected to each other via foreign keys. The key fields of the tables in a lock object form the Lock arguments for the tables. The lock arguments are the basis for formulating the logical condition for identifying the records to be locked.

When activating this lock object, two function modulesB with the names ENQUEUE_<Object_name> and DEQUEUE_<Object_name> are generated.

Example :

Problem :

You wish to prevent a user from being able to change the name of a course or the name of the professor with responsibility for the course at a time when another user is editing the course description (which contains this information).

Solution :

The problem described above can be solved by defining a lock object E_UKURS. This is done by defining primary and secondary tables in the lock object. Table UKURS is check table of table UKRSB, so UKURS should be selected as primary table and UKRSB as secondary table of the lock object.

The Lock argument in this case is the field combination FABNR, KRSNR, and SPRAS (i.e Primary Key Combination).

The Lock mode Shared is to be selected here. This allows several users to access the        data simultaneously in display mode.

The lock mode in the generated function modules for setting (ENQUEUE_E_UKURS) and releasing (DEQUEUE_E_UKURS) locks is therefore set to shared as default, but can be overridden by calling the function modules.

If the function module ENQUEUE_E_UKURS is called with FABNR = '1' and KRSNR = '3', the record for course 3 in faculty 1 is locked in table UKURS. Furthermore, all the course descriptions for this course are locked in table UKRSB since field SPRAS was not specified when the function module was called. In such cases, the lock is made generically for a field which is not defined.

If the function module DEQUEUE_E_UKURS is now called with FABNR = '1', KRSNR = '3' and SPRAS = 'D', the German course description is unlocked. All other course descriptions remain locked.

What is database utility ?

-          Database utility is the interface between the ABAP/4 Dictionary and the underlying the SAP system.

The database utility is the interface between the ABAP/4 Dictionary and the relational database underlying the SAP system. You can call the database utility from the initial screen of the ABAP/4 Dictionary with Utilities ® Database utility.

The database utility allows you to create, delete and convert objects from the ABAP/4 Dictionary in the database.