Controlling Order:
The active Order (index) for a particular work area. Only one Order may control a work area at any time, and it controls the order in which the database is accessed during paging and searching.
Controlling Order :
The active Order (index) for a particular work area. Only one Order may control a work area at any time, and it controls the order in which the database is accessed during paging and searching.
Identity :
A unique value guaranteed by the structure of the data file to reference a specific record in a database even if the record is empty. In the x-base file (.dbf), the identity is the record number; but it could be the value of a unique primary key or even the offset of an array in memory.
Identity Order :
Describes a database arranged by identity. In x-Base, this refers to the physical arrangement of the records in the database in the order in which they were entered (natural order).
Key Expression :
A valid Clipper expression that creates a key value from a single record.
Key Value :
A value that is based on value(s) contained within database fields, associated with a particular record in a database.
Keyed-Pair :
A pair consisting of a key value and an identity.
Lock List :
A list of the records that are currently locked in the work area.
Maintainable scoped Orders :
Scoped (filtered) Orders created using the FOR clause. The FOR condition is stored in the index header. Orders of this type are correctly updated using the expression to reflect record updates, deletions and additions.
Multiple-Order Bag :
An Order Bag that can contain any number of Orders; a multiple-Tag index. The (.cdx) and (.mdx) files are examples of multiple-Order Bags.
Non-maintainable/temporary Orders :
Orders created using the WHILE or NEXT clauses. These Orders are useful because they can be created quickly. However, the conditions in these clauses are not stored in the index header. Therefore, Orders of this type are not correctly updated to reflect record updates, deletions and additions. They are only for temporary use.
Order :
A named mechanism (index) that provides logical access to a database according to the keyed-pairs. This term encompasses both single indexes and the Tags in multiple-Tag indexes.
Orders are not, themselves, data files. They provide access to data that gives the appearance of an ordering of the data in a specific way. This ordering is defined by the relationships between keyed-pairs. An Order does not change the physical (the natural or entry) order of data in a database.
Order Bag :
A container that holds zero or more Orders. Normally a disk or memory file. A traditional index like (.ntx) is an Order Bag that holds only one Order. A multiple-Tag index (.mdx or .cdx) is an Order Bag that holds zero or more Orders. Order Bags may be a memory or disk file.
Order List :
A list of all the Orders available to the database in the specified work area.
Record :
A record in the traditional database paradigm is a row of one or more related columns (fields) of data. In the expanded architecture of Clipper, a record could be data that does not exactly fit this definition.
A record is, in this expanded context, data associated with a single identity. In an x-Base data structure, this corresponds to a row (fields associated with a record number); in other data structures, this may not be the case.
Single-Order Bag :
An Order Bag that can contain only one Order. The (.ntx) and (.ndx) files are examples of single-Order Bags.
Tag :
An Order. A set of keyed-pairs that provides ordered access to the table based on a key value. Usually, an Order in a multiple-Order index (Order).
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