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• The external layer.
• The ABAP/4 layer.
• The database layer.
The external layer is the plane at which the user sees and interacts with the data, that is, the data format in the user interface. This data format is independent of the database system used.
The ABAP/4 layer describes the data formats used by the ABAP/4 processor.
The database layer describes the data formats used in the database.
The Data class determines in which table space the table is stored when it is created in the database.
The Size category describes the probable space requirement of the table in the database.
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 frequently).
• APPL2- Organizational data (customizing data that is entered when system is configured and then rarely changed).
The other two types are:
• USR1 – Intended for customer's own developments.
The values specified for the size category and data class are mapped to database-specific values via control tables.
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.
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).
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).
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.
Each time you create a new object or change an existing object in the ABAP/4 Dictionary, you branch automatically to the Workbench Organizer or correction and transport system.
Domains, Data elements, Tables, Technical settings for tables, Secondary indexes for transparent tables, Structures, Views, Matchcode objects, Matchcode Ids, Lock objects.
Conversion between ABAP/4 data types and the database layer is done within the database interface.
Conversion between the external layer and the ABAP/4 layer is done in the SAP dialog manager DYNP.
ACCP, Char, CLNT, CUKY, CURR, DATS, DESC, FLTP, INT1, INT2, INT4, LANG, LCHR, LRAW, NUMC, PREC, QUAN, RAW, TIMS, UNIT,VARC.
Possible ABAP/4 data types:
D: Date, format YYYYMMDD.
F: Floating-point number in DOUBLE PRECISION (8 bytes).
N: Numerical character string of arbitrary length.
P: Amount of counter field (packed; implementation depends on h/w platform).
S: Time Stamp YYYYMMDDHHMMSS.
V: Character string of variable length, length is given in the first two bytes.
X: Hexadecimal (binary) storage.
You can specify the extent sizes and the table space (physical storage area in the database) in which a transparent table is to be stored by setting the size category and data class.
The correction system manages changes to internal system components. Such as objects of the ABAP/4 Dictionary.
Local objects (Dev class$TMP) are independent of correction and transport system.
Related objects from the ABAP/4 repository are assigned to the same development class. This enables you to correct and transport related objects as a unit.
Data Dictionary is a central source of data in a data management system. Its main function is to support the creation and management of data definitions. 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?
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 s/w development.
• Support form documentation.
• Ensuring that the data definitions are flexible and up-to-date.
The most important features are:
• Integrated to aABAP/4 Development Workbench.
• Active in the runtime environment.
The following information is directly taken from the Data dictionary:
• Information on fields displayed with F1 help.
• Possible entries for fields displayed with F4 help.
• Matchcode and help views search utilities.
• Data elements
• Foreign Keys
• Match codes
• Lock objects.
As a reference table, a system 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.
As a reference table, a system table containing all the valid quantity units is assigned or any other table, which contains a field with the format or quantity units (data type UNIT). This field is called as reference field.
The assignment of the field containing quantity amounts to the reference field is made at runtime. The value in the reference field determines the quantity unit of the amount.
By specifying technical settings we can control how database tables are created in the database. The technical settings allows us to
• Optimize storage space requirements.
• Table access behavior.
• Buffering required.
• Changes to entries logged.
The table's attributes determine who is responsible for maintaining a table and which types of access are allowed for the table. The most important table attributes are:
• Delivery class.
• Table maintenance allowed.
• Activation type.
• 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.
• Append Structures and
• Customizing Includes.
• In case of a substructure, the reference originates in the table itself, in the form of a statement include….
• In case of an append structure, the table itself remains unchanged and the reference originates in the append structure.
Long fields in a table must always be located in the end, as the last field of the table. If a table has an append structure the append line must also be on the last field of the table.
• By specifying fixed values.
• By stipulating a value table.
• Match Code.
• Lock Object.
The tables making up an aggregate object (primary and secondary) are called aggregate object.
• Structure Views.
• Entity Views.
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.
• Match Code Id.
A match code Id is a one character ID that can be a letter or a number.
Yes, the number 0 to 9 are reserved for us to create our own Match Code Ids for a SAP defined Matchcode object.
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.
The following update types are possible:
• Update type A: The matchcode data is updated asynchronously to database changes.
• Update type S: The matchcode data is updated synchronously to database changes.
• Update type P: The matchcode data is updated by the application program.
• Update type I: Access to the matchcode data is managed using a database view.
• Update type L: Access to the matchcode is achieved by calling a function module.
A match code can be built in two different ways:
• Logical structure: The matchcode data is set up temporarily at the moment when the match code is accessed. (Update type I, k).
• Physical Structure: The match code data is physically stored in a separate table in the database. (Update type A, S, P).
• Match code can contain fields from several tables whereas an index can contain fields from only one table.
• Match code objects can be built on transparent tables and pooled and cluster tables.
• A domain describes the technical settings of a table field.
• A domain defines a value range, which sets the permissible data values for the fields, which refers to this domain.
• A single domain can be used as basis for any number of fields that are identical in structure.
• Non-standard conversions from display format to sap internal format and vice-versa are implemented with so called conversion routines.
A data element describes the role played by a domain in a technical context. A data element contains semantic information.
Yes. We can do so by just overwriting the entry in the field domain.
Yes. If you want to specify no data element and therefore no domain for a field, you can enter data type and field length and a short text directly in the table maintenance.
If the value of a field in a table is undefined or unknown, it is called a null value.
Structures are constructed the almost the same way as tables, the only difference using that no database table is generated from them.
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.
• Database View
• Help View
• Projection View
• Maintenance View
When two users simultaneously attempt to access the same data record, this is synchronized by a lock mechanism.
Database utility is the interface between the ABAP/4 Dictionary and the underlying the SAP system.
The basic functions of database utility are:
• Create database objects.
• Delete database objects.
• Adjust database objects to changed ABAP/4 dictionary definition.
It is a tool with which you can make data stored in the ABAP/4 Dictionary available.