Sets, Subsets, and Accesses

Table of Contents

Preparing for Open Disk Technology
Sets
Set Name
Data Set Name
REORGANIZE Clause
Set Type
Key Clause
BINARY, LOGICAL, and EQUIVALENT Comparison Options
DUPLICATES Option
Key Data Option
Set Declaration Example
Subsets
Subset Name
Data Set Name
REORGANIZE Clause
Where Condition
Subset Type
Key Clause
BINARY, LOGICAL, and EQUIVALENT Comparison Options
DUPLICATES Option
Key Data Option
Set Name Identifier
Subset Declaration Examples
Scope Rules for Manual Subsets
Set and Subset Physical Options
AREAS and AREASIZE Options
BUFFERS Option
CHECKSUM Option
Disk/Pack Option
DUMPENCRYPT Option
DUMPSTAMP Option
LOADFACTOR Option
MODULUS Option
NOFTLOCK Option
OPEN PARTITIONS Option
POPULATION Option
PRIME Option
RECORDCOUNT Option
SECURITYGUARD Option
TABLESIZE Option
MEMORY RESIDENT Option
16BITALIAS Option
SECTIONS Option
PHYSICAL SECTIONS Option
Section Bounds Specification
VSSWARN Option
VSS2OPTIMIZE Option
VSS3OPTIMIZE Option
Set and Subset Physical Options Example
Accesses
Access Name
Data Set Name
Key Clause
DUPLICATES Option
MODULUS Option
SECTIONS Option
Section Bounds Specification
Access Examples

Sets, subsets, and accesses perform two functions:

  • They allow data set records to be retrieved rapidly.

  • They represent relationships between data set records.

Three methods are used to retrieve records. The method used depends on whether the structure is a set, subset, or Access. Retrieval Methods explains the retrieval methods and relates the access method to structure type.

Table 10.  Retrieval Methods

Method

Description

Structure Using the Method

Unkeyed

Unkeyed retrieval enables records to be accessed sequentially. User programs should not rely upon retrieving records in any particular order; however, all records are found exactly once.

Unordered list sets, unordered list subsets, bit vector sets, bit vector subsets

Keyed random

Keyed random retrieval is normally used to retrieve records with a particular key value, but sequential retrieval is also allowed. Sequential retrieval does not return the records in any predictable sequence, but each record is returned exactly once.

Accesses to random data sets, index random sets, index random subsets

Keyed sequential

Keyed sequential access enables both random and sequential retrieval. Random retrieval can be used to access records with a specific key value, while sequential retrieval permits the records to be accessed in sequence by key value.

Accesses to direct data sets, Accesses to ordered data sets, index sequential sets, index sequential subsets, ordered list sets, ordered list subsets

One or more retrieval keys must be specified when a set, subset, or Access uses keyed random or keyed sequential access. Keys must be data items within the data set which the set, subset, or Access references. Keys are specified when the database is defined using DASDL syntax.

Manual subsets can be used to represent relationships between data set records. They can be employed to represent networks in the Enterprise Database Server. Manual subsets are maintained by application programs.

The syntax for using sets, subsets, and accesses is discussed under separate headings in the following text.

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