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Metadata is loosely defined as data about data. Metadata is traditionally found in the card catalogues of libraries and is today commonly used to describe three aspects of digital documents and data: 1) definition, 2) structure and 3) administration. By describing the contents and context of data files, the quality of the original data/files is greatly increased. For example, a webpage may include metadata specifying what language it's written in, what tools were used to create it, and where to go for more on the subject, allowing browsers to automatically improve the experience of users.
Metadata is defined as data providing information about one or more other pieces of data, such as:
- Means of creation of the data
- Purpose of the data
- Time and date of creation
- Creator or author of data
- Placement on a computer network where the data was created
- Standards used
For example, a digital image may include metadata that describes how large the picture is, the color depth, the image resolution, when the image was created, and other data. A text document's metadata may contain information about how long the document is, who the author is, when the document was written, and a short summary of the document.
Metadata is data. As such, metadata can be stored and managed in a database, often called a registry or repository. However, it is impossible to identify metadata just by looking at it because a user would not know when data is metadata or just data.
Metadata has been used in various forms as a means of cataloging archived information. The Dewey Decimal System employed by libraries for the classification of library materials is an early example of metadata usage. Library catalogues used small 3x5 inch cards to display a book's title, author, subject matter, and a brief plot synopsis along with an abbreviated alpha-numeric identification system which indicated the physical location of the book within the library's shelves. Such data helps classify, aggregate, identify, and locate a particular book. Another form of older metadata collection is the use by US Census Bureau of what is known as the "Long Form." The Long Form asks questions that are used to create demographic data to create patterns and to find patterns of distribution.  The term was coined in 1968 by Philip Bagley, one of the pioneers of computerized document retrieval. Since then the fields of information management, information science, information technology, librarianship and GIS have widely adopted the term. In these fields the word metadata is defined as "data about data". While this is the generally accepted definition, various disciplines have adopted their own more specific explanation and uses of the term.
For the purposes of this article, an "object" refers to any of the following:
- A physical item such as a book, CD, DVD, map, chair, table, flower pot, etc.
- An electronic file such as a digital image, digital photo, document, program file, database table, etc.
Metadata may be written into a digital photo file that will identify who owns it, copyright & contact information, what camera created the file, along with exposure information and descriptive information such as keywords about the photo, making the file searchable on the computer and/or the Internet. Some metadata is written by the camera and some is input by the photographer and/or software after downloading to a computer.
Photographic Metadata Standards are governed by organizations that develop the following standards. They include, but are not limited to:
- IPTC Information Interchange Model IIM (International Press Telecommunications Council),
- IPTC Core Schema for XMP,
- XMP ' Extensible Metadata Platform (an Adobe standard)
- Exif ' Exchangeable image file format, Maintained by CIPA (Camera & Imaging Products Association) and published by JEITA (Japan Electronics and Information Technology Industries Association)
- Dublin Core (Dublin Core Metadata Initiative ' DCMI)
- PLUS (Picture Licensing Universal System)
Metadata is particularly useful in video, where information about its contents (such as transcripts of conversations and text descriptions of its scenes) are not directly understandable by a computer, but where efficient search is desirable.
 Web pages
Web pages often include metadata in the form of meta tags. Description and keywords meta tags are commonly used to describe the Web page's content. Most search engines use this data when adding pages to their search index.
 Creation of metadata
Metadata can be created either by automated information processing or by manual work. Elementary metadata captured by computers can include information about when a file was created, who created it, when it was last updated, file size and file extension.
 Metadata structures
Metadata is typically structured according to a standardised concept using a well defined metadata scheme, including: metadata standards and metadata models. Tools such as controlled vocabularies, taxonomies, thesauri, data dictionaries and metadata registries can be used to apply further standardisation to the metadata.
 Metadata syntax
Metadata syntax refers to the rules created to structure the fields or elements of metadata. A single metadata scheme may be expressed in a number of different markup or programming languages, each of which requires a different syntax. For example, Dublin Core may be expressed in plain text, HTML, XML and RDF.
 Metadata types
The metadata application is manifold covering a large variety of fields of application there are nothing but specialised and well accepted models to specify types of metadata. Bretheron & Singley (1994) distinguish between two distinct classes: structural/control metadata and guide metadata. Structural metadata is used to describe the structure of computer systems such as tables, columns and indexes. Guide metadata is used to help humans find specific items and is usually expressed as a set of keywords in a natural language. According to Ralph Kimball metadata can be divided into 2 similar categories'Technical metadata and Business metadata. Technical metadata correspond to internal metadata, business metadata to external metadata. Kimball adds a third category named Process metadata. On the other hand, NISO distinguishes between three types of metadata: descriptive, structural and administrative.  Descriptive metadata is the information used to search and locate an object such as title, author, subjects, keywords, publisher; structural metadata gives a description of how the components of the object are organised; and administrative metadata refers to the technical information including file type. Two sub-types of administrative metadata are rights management metadata and preservation metadata.
 Hierarchical, linear and planar schemata
Metadata schemas can be hierarchical in nature where relationships exist between metadata elements and elements are nested so that parent-child relationships exist between the elements. An example of a hierarchical metadata schema is the IEEE LOM schema where metadata elements may belong to a parent metadata element. Metadata schemas can also be one dimensional, or linear, where each element is completely discrete from other elements and classified according to one dimension only. An example of a linear metadata schema is Dublin Core schema which is one dimensional. Metadata schemas are often two dimensional, or planar, where each element is completely discrete from other elements but classified according to two orthogonal dimensions.
 Metadata hypermapping
In all cases where the metadata schemata exceed the planar depiction, some type of hypermapping is required to enable display and view of metadata according to chosen aspect and to serve special views. Hypermapping frequently applies to layering of geographical and geological information overlays.
Granularity is a term that applies to data as well as to metadata. The degree to which metadata is structured is referred to as its granularity. Metadata with a high granularity allows for deeper structured information and enables greater levels of technical manipulation however, a lower level of granularity means that metadata can be created for considerably lower costs but will not provide as detailed information. The major impact of granularity is not only on creation and capture, but moreover on maintenance. As soon as the metadata structures get outdated, the access to the referred data will get outdated. Hence granularity shall take into account the effort to create as well as the effort to maintain.
 Metadata standards
International standards apply to metadata. Much work is being accomplished in the national and international standards communities, especially ANSI (American National Standards Institute) and ISO (International Organization for Standardization) to reach consensus on standardizing metadata and registries.
The core standard is ISO/IEC 11179-1:2004  and subsequent standards (see ISO/IEC 11179). All yet published registrations according to this standard cover just the definition of metadata and do not serve the structuring of metadata storage or retrieval neither any administrative standardisation.
 Metadata usage
 Data Virtualization
Data Virtualization has emerged as the new software technology to complete the virtualization stack in the enterprise. Metadata is used in Data Virtualization servers which are enterprise infrastructure components, along side with Database and Application servers. Metadata in these servers is saved as persistent repository and describes business objects in various enterprise systems and applications.
 Statistics and census services
Standardisation work has had a large impact on efforts to build metadata systems in the statistical community. Several metadata standards are described, and their importance to statistical agencies is discussed. Applications of the standards at the Census Bureau, Environmental Protection Agency, Bureau of Labor Statistics, Statistics Canada, and many others are described. Emphasis is on the impact a metadata registry can have in a statistical agency.
 Library and information science
Libraries employ metadata in library catalogues, most commonly as part of an Integrated Library Management System. Metadata is obtained by cataloguing resources such as books, periodicals, DVDs, web pages or digital images. This data is stored in the integrated library management system, ILMS, using the MARC metadata standard. The purpose is to direct patrons to the physical or electronic location of items or areas they seek as well as to provide a description of the item/s in question.
More recent and specialised instances of library metadata include the establishment of digital libraries including e-print repositories and digital image libraries. While often based on library principles the focus on non-librarian use, espcially in providing metadata means they do not follow traditional or common cataloguing approaches. Given the custom nature of included materials metadata fields are often specially created e.g. taxonomic classification fields, location fields, keywords or copyright statement. Standard file information such as filesize and format are usually automatically included.
Standardisation for library operation has been a key topic in international standardisation (ISO) for decades. Standards for metadata in digital libraries include Dublin Core, METS, MODS, DDI, ISO standard Digital Object Identifier (DOI), ISO standard Uniform Resource Name (URN), PREMIS schema, and OAI-PMH. Leading libraries in the world give hints on their metadata standards strategies.
 Metadata and the law
 United States
Problems involving metadata in litigation in the United States are becoming widespread. Courts have looked at various questions involving metadata, including the discoverability of metadata by parties. Although the Federal Rules of Civil Procedure have only specified rules about electronic documents, subsequent case law has elaborated on the requirement of parties to reveal metadata. In October 2009, the Arizona Supreme Court has ruled that metadata records are public record.
Document Metadata has proven particularly important in legal environments in which litigation has requested metadata, which can include sensitive information detrimental to a party in court.
Using metadata removal tools to "clean" documents can mitigate the risks of unwittingly sending sensitive data. This process partially (see Data remanence) protects law firms from potentially damaging leaking of sensitive data through Electronic Discovery.
 Metadata in healthcare
Australian researches in medicine started a lot of metadata definition for applications in health care. That approach offers the first recognised attempt to adhere to international standards in medical sciences instead of defining a proprietary standard under the WHO umbrella first.
The medical community yet did not approve the need to follow metadata standards despite respective research.
 Metadata and data warehousing
Data warehouse (DW) is a repository of an organization's electronically stored data. Data warehouses are designed to manage and store the data whereas the Business Intelligence (BI) focuses on the usage of data to facilitate reporting and analysis.
The purpose of a data warehouse is to house standardized, structured, consistent, integrated, correct, cleansed and timely data, extracted from various operational systems in an organization. The extracted data is integrated in the data warehouse environment in order to provide an enterprise wide perspective, one version of the truth. Data is structured in a way to specifically address the reporting and analytic requirements.
An essential component of a data warehouse/business intelligence system is the metadata and tools to manage and retrieve metadata. Ralph Kimball describes metadata as the DNA of the data warehouse as metadata defines the elements of the data warehouse and how they work together.
Kimball et al. refers to three main categories of metadata: Technical metadata, business metadata and process metadata. Technical metadata is primarily definitional while business metadata and process metadata are primarily descriptive. Keep in mind that the categories sometimes overlap.
- Technical metadata defines the objects and processes in a DW/BI system, as seen from a technical point of view. The technical metadata includes the system metadata which defines the data structures such as: Tables, fields, data types, indexes and partitions in the relational engine, and databases, dimensions, measures, and data mining models. Technical metadata defines the data model and the way it is displayed for the users, with the reports, schedules, distribution lists and user security rights.
- Business metadata is content from the data warehouse described in more user friendly terms. The business metadata tells you what data you have, where it comes from, what it means and what its relationship is to other data in the data warehouse. Business metadata may also serves as documentation for the DW/BI system. Users who browse the data warehouse are primarily viewing the business metadata.
- Process metadata is used to describe the results of various operations in the data warehouse. Within the ETL process all key data from tasks are logged on execution. This includes start time, end time, CPU seconds used, disk reads, disk writes and rows processed. When troubleshooting the ETL or query process, this sort of data becomes valuable. Process metadata is the fact measurement when building and using a DW/BI system. Some organizations make a living out of collecting and selling this sort of data to companies - in that case the process metadata becomes the business metadata for the fact and dimension tables. Process metadata is in interest of business people who can use the data to identify the users of their products, which products they are using and what level of service they are receiving.
 Metadata on the Internet
The HTML format used to define web pages allows for the inclusion of a variety of types of metadata, from basic descriptive text, dates and keywords to further advanced metadata schemes such as the Dublin Core, e-GMS, and AGLS standards. Pages can also be geotagged with coordinates. Metadata may be included in the page's header or in a separate file. Microformats allow metadata to be added to on-page data in a way that users don't see, but computers can readily access.
Interestingly, many search engines are cautious about using metadata in their ranking algorithms due to exploitation of metadata and the practice of search engine optimization, SEO, to improve rankings. See Meta element article for further discussion.
 Geospatial metadata
Metadata that describe geographic objects (such as datasets, maps, features, or simply documents with a geospatial component) have a history dating back to at least 1994 (refer MIT Library page on FGDC Metadata). This class of metadata is described more fully on the Geospatial metadata page.
 Metadata on CDs and DVDs
CDs such as recordings of music will carry a layer of metadata about the recordings such as dates, artist, genre, copyright owner, etc. The metadata, not normally displayed by CD players, can be accessed and displayed by specialized music playback and/or editing applications.
 Cloud applications
With the availability of Cloud applications, which include those to add metadata to content, metadata is increasingly available over the Internet.
 Metadata administration and management
 Metadata storage
Metadata can be stored either internally, in the same file as the data, or externally, in a separate file. Metadata that is embedded with content is called embedded metadata. A data repository typically stores the metadata detached from the data. Both ways have advantages and disadvantages:
- Internal storage allows transferring metadata together with the data it describes; thus, metadata is always at hand and can be manipulated easily. This method creates high redundancy and does not allow holding metadata together.
- External storage allows bundling metadata, for example in a database, for more efficient searching. There is no redundancy and metadata can be transferred simultaneously when using streaming. However, as most formats use URIs for that purpose, the method of how the metadata is linked to its data should be treated with care. What if a resource does not have a URI (resources on a local hard disk or web pages that are created on-the-fly using a content management system)? What if metadata can only be evaluated if there is a connection to the Web, especially when using RDF? How to realize that a resource is replaced by another with the same name but different content?
Moreover, there is the question of data format: storing metadata in a human-readable format such as XML can be useful because users can understand and edit it without specialized tools. On the other hand, these formats are not optimized for storage capacity; it may be useful to store metadata in a binary, non-human-readable format instead to speed up transfer and save memory.
 Database management
Each relational database system has its own mechanisms for storing metadata. Examples of relational-database metadata include:
- Tables of all tables in a database, their names, sizes and number of rows in each table.
- Tables of columns in each database, what tables they are used in, and the type of data stored in each column.
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. Programmatic access to metadata is possible using APIs such as JDBC, or SchemaCrawler.
 See also
- ^ METADATA STANDARDS AND METADATA REGISTRIES: AN OVERVIEW
- ^ National Archives of Australia (2002). "AGLS Metadata Element Set - Part 2: Usage Guide - A non-technical guide to using AGLS metadata for describing resources". http://www.naa.gov.au/records-management/publications/agls-element.aspx. Retrieved 17 March 2010.
- ^ Bagley, Philip (Nov 1968), Extension of programming language concepts, Philadelphia: University City Science Center
- ^ "The notion of "metadata" introduced by Bagley". Solntseff, N+1; Yezerski, A (1974), A survey of extensible programming languages, Annual Review in Automatic Programming, 7, Elsevier Science Ltd, pp. 267'307, doi:10.1016/0066-4138(74)90001-9
- ^ a b NISO. "Understanding Metadata". NISO Press. http://www.niso.org/publications/press/UnderstandingMetadata.pdf. Retrieved 5 January 2010.
- ^ Cathro, Warwick (1997). "Metadata: an overview". http://www.nla.gov.au/nla/staffpaper/cathro3.html. Retrieved 6 January 2010.
- ^ DCMI (5 Oct 2009). "Semantic Recommendations". http://dublincore.org/specifications/. Retrieved 6 January 2010.
- ^ Bretherton, F. P.; Singley, P.T. (1994). "Metadata: A User's View, Proceedings of the International Conference on Very Large Data Bases (VLDB)". pp. 1091'1094.
- ^ "Types of Metadata". University of Melbourne. 15 August 2006. http://www.infodiv.unimelb.edu.au/metadata/add_info.html. Retrieved 6 January 2010.
- ^ [www.isprs.org/proceedings/XXXII/part4/www.ifp.uni.../kuebler51.pdf THE DESIGN AND DEVELOPMENT OF A GEOLOGIC HYPERMAP PROTOTYPE]
- ^ ISO/IEC 11179-1:2004 Information technology - Metadata registries (MDR) - Part 1: Framework
- ^ Library of Congress Washington DC on metadata
- ^ [www.d-nb.de/standardisierung/.../metadaten.htm Deutsche Nationalbibliothek Frankfurt on metadata]
- ^ Gelzer, Reed D. (February 2008). "Metadata, Law, and the Real World: Slowly, the Three Are Merging". Journal of AHIMA (American Health Information Management Association) 79 (2): 56'57, 64. http://library.ahima.org/xpedio/groups/public/documents/ahima/bok1_036537.hcsp?dDocName=bok1_036537. Retrieved 8 January 2010.
- ^ Walsh, Jim (30 October 2009). "Ariz. Supreme Court rules electronic data is public record". The Arizona Republic (Arizona, United States). http://www.azcentral.com/arizonarepublic/local/articles/2009/10/30/20091030metadata1030.html. Retrieved 8 January 2010.
- ^ M. Löbe, M. Knuth, R. Mücke TIM: A Semantic Web Application for the Specification of Metadata Items in Clinical Research, CEUR-WS.org, urn:nbn:de:0074-559-9
- ^ Inmon, W.H. Tech Topic: What is a Data Warehouse? Prism Solutions. Volume 1. 1995. (http://en.wikipedia.orghttp://en.wikipedia.org/wiki/Data_warehouse)
- ^ Ralph Kimball,The Data Warehouse Lifecycle Toolkit, Second Edition. New York, Wiley, 2008, ISBN 978-0-470-14977-5, page 10, 115'117, 131'132, 140, 154'155
- ^ Kimball et al., The Data Warehouse Lifecycle Toolkit, Second Edition. New York, Wiley, 2008, ISBN 978-0-470-14977-5, 116'117
- ^ National Archives of Australia, AGLS Metadata Standard, accessed 7 January 2010, 
- ^ Sualeh Fatehi. "SchemaCrawler". SourceForge. http://schemacrawler.sourceforge.net/.
 External links
Creating the data warehouse
Using the data warehouse