Metadata, or "data about data," is a new word based on an old concept. In libraries, cataloging is the process of creating metadata. A card-catalog containing information about a book is a simple example of metadata describing characteristics of an information resource. Regardless of old concepts, the term "metadata" is used particularly in the context of modern information systems and electronic networks.
Metadata has been defined in various ways. Tim Berners Lee defined metadata as "machine-readable information about electronic resources or other things" (1997). This definition addresses metadata applied to electronic resources and refers to "data" in a broader scope that includes not only textual, but non-textual information such as graphics, music, or anything likely to appear in an electronic format. It is clear that metadata can be deployed for non-digital objects too. But as mentioned, it most commonly refers to digital information especially on the Web.
Another definition of metadata is that assigned by the DESIRE project: "Data associated with objects which relieves their potential users of having to have full advance knowledge of their existence and characteristics" (2000). The basic purposes of metadata are covered by this definition, including a wide range of operations such as discovery, description, management, and long-term preservation of information resources. Metadata also facilitates and improves the information retrieval process (when examined with a view towards recall and precision criteria), by identifying the major concepts of the information resource.
Main Types of Metadata
The abovementioned definitions address three main types of metadata. According to the North Carolina ECHO (Exploring Cultural Heritage Online) Guidelines for Digitization (2006), these are:
1. Descriptive metadata describes a resource for purposes such as indexing, discovery and identification. It can include elements such as title, abstract, author, and keywords.
2. Structural metadata includes information employed to display and navigate digital resources; also includes information on internal organization of the digital resource. Structural metadata might contain information such as the structural divisions of a resource that indicates how compound objects are put together--for example, how pages are ordered to form chapters, or information about sub-object relationships such as individual diary entries in a diary section.
3. Administrative metadata provides information to help manage a resource, such as the data and the state in which the resource was created , file type and also right management information (which deals with intellectual property rights). Administrative metadata might include technical information, such as the resolution at which the images were scanned, the hardware and software used to produce the image, compression information, pixel dimensions, etc. Administrative metadata may also assist in the long-term preservation of digital resources (which contains information needed to archive and preserve a resource). It is mentionable that sometimes Rights management and Preservation information are listed as separate metadata types (NISO, 2004).
Other categorizations of metadata exist. One of them is as follow: Administrative, Descriptive, Preservation, Technical, and Use metadata (Gill, Gilliland, & Woodley, 2000).
The essential information that metadata gives about a resource is: how it was gathered, the purpose of its gathering, manifestation and manipulation, intellectual properties, and content descriptions such as title, subject, and abstract. This information is represented by a limited number of elements. Each element can take one or more values. These elements are originally defined by one of the metadata schemas. The elements must be embedded in an encoding structure-- such as HTML or XML--in one of two ways: in the object itself or separately. …