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Oracle and IBM Db2 provide a construct explicitly named CLOB, [1] [2] and the majority of other database systems support some form of the concept, often labeled as text, memo or long character fields. CLOBs usually have very high size-limits, of the order of gigabytes. The tradeoff for the capacity is usually limited access methods.
Descriptive metadata is typically used for discovery and identification, as information to search and locate an object, such as title, authors, subjects, keywords, and publisher. Structural metadata describes how the components of an object are organized. An example of structural metadata would be how pages are ordered to form chapters of a book.
SQL was initially developed at IBM by Donald D. Chamberlin and Raymond F. Boyce after learning about the relational model from Edgar F. Codd [12] in the early 1970s. [13] This version, initially called SEQUEL (Structured English Query Language), was designed to manipulate and retrieve data stored in IBM's original quasirelational database management system, System R, which a group at IBM San ...
The SQL standard specifies a uniform means to access the catalog, called the INFORMATION_SCHEMA, but not all databases follow this, even if they implement other aspects of the SQL standard. For an example of database-specific metadata access methods, see Oracle metadata .
The terms data dictionary and data repository indicate a more general software utility than a catalogue. A catalogue is closely coupled with the DBMS software. It provides the information stored in it to the user and the DBA, but it is mainly accessed by the various software modules of the DBMS itself, such as DDL and DML compilers, the query optimiser, the transaction processor, report ...
SQL includes operators and functions for calculating values on stored values. SQL allows the use of expressions in the select list to project data, as in the following example, which returns a list of books that cost more than 100.00 with an additional sales_tax column containing a sales tax figure calculated at 6% of the price.
Structural metadata documents relationships within and among objects through elements such as links to other components (e.g., how pages are put together to form chapters). Administrative metadata helps to manage information resources through elements such as version number, archiving date, and other technical information for purposes of file ...
Metadatabase is a database model for (1) metadata management, (2) global query of independent databases, and (3) distributed data processing.