Meta Data:
Meta data 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. Meta data 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. Meta data can be stored either internally, in the same file as the data or externally, in a separate area. Both have advantages and disadvantages. I f the data is stored internally, the meta data 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 most be used, such as Uniform Resource Identifier(URI) to get to the meta data, if this format is not used the meta data becomes in accessible. 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 use 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 changed structure is not necessary.
UPDATE
Metadata
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) Meta data 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 to database design, it allows for increased processing power, due to the fact that it can help create pointers and indexes.
Added by
Rob, P., & Coronel, C. (2009). Database Systems Design, Implementation, And Management. Boston: Course Technology.
Sheldon, T. (2001). Metadata. Retrieved 12 03, 2009, from Linktionary: http://www.linktionary.com/m/metadata.html
UPDATE 10/14/2011
Definition
Metadata is defined as data that describes other data. Metadata can be divided into two main types: structural and descriptive. Structural metadatadescribes the design structure and their specifications. This type of metadata describes the containers of data within a database. Descriptive metadatadescribes instances of application data. This is the type of metadata that is traditionally spoken of and described as “data about the data.” A third type is sometime identified called Adminitstrative metadata. Administrative metadata provides information that helps to manage other information, such as when and how a resource was created, file types and other technical information.
Metadata makes it easier to retrieve, use, or manage information resources by providing users with information that adds context to the data they’re working with. Metadata can describe information at any level of aggregation, including collections, single resources, or component part of a single resource. Metadata can be embedded into a digital object or can be stored separately
Web pages contain metadata called metatags.
Examples:
e.g. A .mp3 audio file contains metadata that describes the length of the song, the artist, etc.
e.g. A word document contains metadata such as last time modified, length, author, etc.
References
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