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Implementation of Data Independence

IP.com Disclosure Number: IPCOM000074720D
Original Publication Date: 1971-Jun-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 4 page(s) / 116K

Publishing Venue

IBM

Related People

Otte, FH: AUTHOR

Abstract

Definitions. Data Independence is the ability of an applications programmer to construct his own logical record (LR) from a list of field names. A sequential collection of LR's is a logical file. The programmer is not aware of the physical location of the fields in physical records and physical files. Query (see (1) in the flowchart).

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Implementation of Data Independence

Definitions. Data Independence is the ability of an applications programmer to construct his own logical record (LR) from a list of field names. A sequential collection of LR's is a logical file. The programmer is not aware of the physical location of the fields in physical records and physical files. Query (see (1) in the flowchart).

The programmer specifies the fields (presentation criteria) he wants for his LR and the sequence he desires for his logical file. Additionally, he may designate fields (selection criteria), that must have definite values in order to make the logical record acceptable. Relationships.

Fields in the same physical record are naturally related. Files have different record layouts, but there are fields with the same meaning in different files. These are the link fields. These links connect file-to-file and thereby relate any field in the data base to any other field. Instant Internal Logical Record.

Internally the LR - defined by presentation criteria - is expanded to the Internal Logical Record (ILR). Fields mentioned in the selection criteria must be added if they are not part of the presentation criteria. Link fields must be included if more than one physical file is to be accessed. A field in the ILR then can have any or all of three attributes: (1) Presentation field, (2) Selection field,
(3) Link field. Retrieval Algorithm (see (2) in the flowchart).

Since not all fields of the ILR can be retrieved with a single physical read, an orderly process must be established for the multiple reads. The object of this algorithm is a minimum of searching. One must establish which physical files must be accessed and in what order. This is called the Access Chain. Moreover, each file is to be accessed in a certain sequence via indexes and value(s). One approach would be to start with the field, the value of which determines the sequence of the basic LR. In a query environment, however, retrieval of selection fields must be first in the algorithm. Retrieval (see (3) in the flowchart).

Once the access chain has been established, the retrieval of logical records can begin. After the first physical record has been read, some field values of the physical record are transferred...