NULL A field that (Web site developers) has never been initialized with
NULL A field that has never been initialized with any value. A NULL field setting allows a field to contain nothing when a record is created or changed in a table. Number A numeric datatype allowing only numbers of various formats. Number crunching Computer jargon for large quantities of extremely complex calculations. Object In object methodology, the creation (instantiation) of a class at run-time, such that multiple object instances can be created from a class. An object is also a generic term applied to anything tangible, such as a table in a relational database. Object database model A model that provides a three-dimensional structure to data where any item in a database can be retrieved from any point very rapidly. Whereas the relational database model lends itself to retrieval of groups of records in two dimensions, the object database model is very efficient for finding unique items. Consequently, the object database model performs very poorly when retrieving more than a single item, at which the relational database model is very good. Object-relational database model The object-relational database model includes minimal aspects of the object database model into the relational database model. In some respects, the object-relational database model was created in answer to conflicting capabilities of relational and object database models and also as a commercial competitor to the object database model. The object database model is somewhat spherical in nature, allowing access to unique elements anywhere within a database structure, with extremely high performance. The object database model performs extremely poorly when retrieving more than a single data item. The relational database model, on the other hand, contains records of data in tables across two dimensions. The relational database model is best suited for retrieval of groups of data but can also be used to access unique data items fairly efficiently. OLAP See Online Analytical Processing. OLTP See Online Transaction Processing. ON clause The ON clause is an ANSI standard join format that allows exact field join specifications when you want to include one or more fields in a join, which have different names in different tables. One-to-many relationship The relationship between two tables dictated by having one record in one table, and many related records in another table. One-to-one relationship The relationship between two tables dictated by having one record in each table, and not more than one record in either table, related back to the other table. Online Analytical Processing (OLAP) A functionality that provides rapid interactive analysis of data into multiple dimensions, usually involving extremely large databases. The objective of analysis is to highlight trends, patterns and exceptions. Online Transaction Processing OLTP) Databases that were devised to cater for the enormous concurrency requirements of Internet (online) applications. OLTP databases cause problems with concurrency. The number of users that can be reached over the Internet is an unimaginable order of magnitude larger than that of an in-house company client-server database. Thus, the concurrency requirements for OLTP database models explodes well beyond the scope of previous experience with client-server databases. 414 Glossary
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