Encyclopedia of Computer Science and Technology

data mining 135Further ReadingArimura, Mitsuharu. “Mitsuharu Arimura’s Bookmarks on SourceCoding/Data Compression.” Available online. URL: http://www.hn.is.uec.ac.jp/~arimura/compression_links.html.Accessed July 8, 2007.“Data Compression Reference Center.” Available online. URL:http://www.rasip.fer.hr/_research/compress/index.html.Accessed July 8, 2007.Saloman, David. Data Compression: The Complete Reference. 4th ed.New York: Springer-Verlag, 2006.Sayood, Khalid. Introduction to Data Compression. 3rd ed. SanFrancisco: Morgan Kaufmann, 2005.data conversionThe developer of each application program that writes datafiles must define a format for the data. The format mustbe able to preserve all the features that are supported bythe program. For example, a word processing program willinclude special codes for font selection, typestyles (such asbold or italic), margin settings, and so on.In most markets there are more than one vendor, sothere is the potential for users to encounter the need toconvert files such as word processing documents from onevendor’s format to another. For example, a Microsoft Worduser needing to send a document to a user who has Word-Perfect, or the user may encounter another user who alsohas Microsoft Word, but a later version.There are some ways in which vendors can relieve someof their users’ file conversion issues (and thus potentialcustomer dissatisfaction). Vendors often include facilities toread files created by their major rivals’ products, and to savefiles back into those formats. This enables users to exchangefiles. Sometimes the converted document will look exactlylike the original, but in some cases there is no equivalencebetween a feature (and thus a code) in one application and afeature in the other application. In that case the formattingor other feature may not carry over into the converted version,or may be only partially successful.Vendors generally make a new version of an applicationdownwardly compatible with previous versions (seealso compatability and portability). This means that thenew version can read files created with the earlier versions.(After all, users would not be happy if none of their existingdocuments were accessible to their new software!) Similarly,there is usually a way to save a file from the later version inthe format of an earlier version, though features added in thelater version will not be available in the earlier format.Another strategy for exchanging otherwise incompatiblefiles is to find some third format that both applications canread. Thus Rich Text Format (RTF), a format that includesmost generic document features, is supported by most modernword processors. A user can thus export a file as RTFand the user of a different program will be able to read it(see rtf). Similarly, many database and other programs canexport files as a series of data values separated by commas(comma-delimited files), and the files can be then read by adifferent program and converted to its “native” format.A variety of format conversion utilities are available aseither commercial software or shareware. There are also businessesthat specialize in data conversion. While their servicescan be expensive, using them may be the best way to convertlarge numbers of files, rather than having to individuallyload and save them. Data conversion services can also handlemany “ancient” data files from the 1970s or even early 1980swhose formats are no longer supported by current software.Further ReadingHeuser, Werner. “Data Conversion and Migration Tools.” Availableonline. URL: http://dataconv.org/. Accessed July 8, 2007.“Media Conversion: Online File Conversions.” Available online.URL: http://www.iconv.com/. Accessed July 8, 2007.data dictionaryA modern enterprise database system can contain hundredsof separate data items, each with important characteristicssuch as field types and lengths, rules for validating the data,and links to various databases that use that item (see databasemanagement system). There can also be many differentviews or ways of organizing subsets of the data, and storedprocedures (program code modules) used to perform variousdata processing functions. A developer who is creatingor modifying applications that deal with such a vast databasewill often need to check on the relationships between dataelements, views, procedures, and other aspects of the system.One fortunate characteristic of computer science is thatmany tools can be applied to themselves, often because thecontents of a program is itself a collection of data. Thus, it ispossible to create a database that keeps track of the elementsof another database. Such a database is sometimes called adata dictionary. A data dictionary system can be developedin the same way as any other database, but many databasedevelopment systems now contain built-in facilities for generatingdata dictionary entries as new data items are defined,and updating definitions as items are linked together and newviews or stored procedures are defined. (A similar approachcan be seen in some software development systems that createa database of objects defined within programs, in order topreserve information that can be useful during debugging.)Data dictionaries are particularly important for creatingdata warehouses (see data warehouse), which are largecollections of data items that are stored together with theprocedures for manipulating and analyzing them.Further ReadingKreines, David. Oracle Data Dictionary Pocket Reference. Sebastapol,Calif.: O’Reilly Media, 2003.Pelzer, Trudy. “MySQL 5.0 New Features: Data Dictionary.”Available online. URL: http://dev.mysql.com/tech-resources/articles/mysql-datadictionary.html. Accessed July 8, 2007.data glove See haptics.data miningThe process of analyzing existing databases in order to finduseful information is called data mining. Generally, a database,whether scientific or commercial, is designed for a