Metadata is "data about data". In database terminology, this set of metadata is referred to as the catalog. The SQL standard specifies a uniform means to access the catalog, called the information schema, but not all databases implement it, even if they implement other aspects of the SQL standard. For an example of database-specific metadata access methods, see Oracle metadata.
Meta Data:
Metadata is “data about data”. An item of metadata describes the specific characteristics about an individual data item. In databases, metadata describes the structural components of tables and their elements. For example, metadata about an element could include data types, name of data, size and many more characteristics about that element. It would also give information about the tables the database is storing, information, such as length of fields, number of columns, where the tables are located and other pertinent information. One of the main uses for met data is to provide a link between the information creator and the information users. Metadata allows the users to speed up the search for individual data. This is done by being able to set parameter for searches, allowing the filtering of unwanted information. Metadata can be stored either internally, in the same file as the data or externally, in a separate area. Both have advantages and disadvantages. If the data is stored internally, the metadata is together with the data making more easily accessible to view or change. However, this method creates high redundancy. If metadata is stored externally, the searches can become more efficient. There is no redundancy but getting to this metadata may be a little more technical. There are certain formats that must be used, such as Uniform Resource Identifier(URI) to get to the metadata if this format is not used the metadata becomes inaccessible. All the metadata is stored in a data dictionary or a system catalog. All programs that access data in the database work through a DBMS. The DBMS uses the data dictionary to look up the required components and relationships. Any changes made to the database structure are automatically recorded in the data dictionary. This makes the data dictionary manager’s job a lot easier because any modification of programs that are affected by the changed structure is not necessary.
Metadata at the most basic level is simply defined as “data about data”. An item of metadata describes the specific characteristics about an individual data item. In the database realm, metadata is defined as, “data about data, through which the end-user data are integrated and managed.” (Rob & Coronel, 2009) Metadata in a database typically store the relationships that link up numerous pieces of data. “Metadata names these fields describes the size of the fields, and may put restrictions on what can go in the field (for example, numbers only).” (Sheldon, 2001).
“Therefore, metadata is information about how data is extracted, and how it may be transformed. It is also about indexing and creating pointers into data. Database design is all about defining metadata schemas.” (Sheldon, 2001) Metadata can be stored either internally, in the same file as the data, or externally, in a separate area. If the data is stored internally, the metadata is together with the data, making it more easily accessible to view or change. However, this method creates high redundancy. If metadata is stored externally, the searches can become more efficient. There is no redundancy but getting to this metadata may be a little more technical.
All the metadata is stored in a data dictionary or a system catalog. The data dictionary is most typically an external document that is created in a spreadsheet type of document that stores the conceptual design ideas for the database schema. The data dictionary also contains the general format that the data, and in effect the metadata, should be. Metadata is an essential aspect of database design, it allows for increased processing power, due to the fact that it can help create pointers and indexes.
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