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[1] For referential integrity to hold in a relational database, any column in a base table that is declared a foreign key can only contain either null values or values from a parent table's primary key or a candidate key. [2] In other words, when a foreign key value is used it must reference a valid, existing primary key in the parent table.
A database index is a data structure that improves the speed of data retrieval operations on a database table at the cost of additional writes and storage space to maintain the index data structure. Indexes are used to quickly locate data without having to search every row in a database table every time said table is accessed.
A bitmap index is a special kind of database index that uses bitmaps. Bitmap indexes have traditionally been considered to work well for low- cardinality columns , which have a modest number of distinct values, either absolutely, or relative to the number of records that contain the data.
Microsoft Access has two built-in utilities, Database Splitter [53] and Linked Table Manager, to facilitate this architecture. Linked tables in Access use absolute paths rather than relative paths, so the development environment either has to have the same path as the production environment or a "dynamic-linker" routine can be written in VBA.
The closeness of a match is measured in terms of the number of primitive operations necessary to convert the string into an exact match. This number is called the edit distance between the string and the pattern. The usual primitive operations are: [1] insertion: cot → coat; deletion: coat → cot; substitution: coat → cost
A database table can be thought of as consisting of rows and columns. [1] Each row in a table represents a set of related data, and every row in the table has the same structure. For example, in a table that represents companies, each row might represent a single company. Columns might represent things like company name, address, etc.
Sequential access is a term describing a group of elements (such as data in a memory array or a disk file or on magnetic-tape data storage) being accessed in a predetermined, ordered sequence. It is the opposite of random access , the ability to access an arbitrary element of a sequence as easily and efficiently as any other at any time.
An access descriptor contains permission bits and a 26-bit object index; the object index is an index into a table of object descriptors, giving an object type, an object length, and a physical address for the object's data, a page table for the object, or the top-level page table for a two-level page table for the object, depending on the ...