Aggregation A complex entity composed of less complex entities.
AOM Asset Oriented Modeling (see Chapter 2). A modeling method based on regular grammars, and unifying the dual concepts of entities and relationships into the single concept of assets.
API Application Programming Interface. A description of the features of a program module for the client software wanting to use this module.
Asset In AOM an asset is an abstract notion for any object or relationship between objects that we want to include in a model.
Association A relationship that somehow correlates entities with others.
Browser A user agent that presents HTML or XML pages on a computer screen and supports navigation over the World Wide Web.
Business object A business object represents a real-world entity from the business problem domain that plays a role within the business scenario.
Business process A networklike construct of business objects to describe a complex value creating (or servicing) business activity.
Canonical form A preferred syntax and lexical representation for a given content. The canonical form allows comparison of objects by their string representation: When their string representations are equal, their content is equal, too.
CASE Computer-aided software engineering. CASE tools support the design of software systems and can automatically generate certain parts of the implementation. Roundtrip engineering allows changes in the implementation to be reflected back into the conceptual design.
Constraint A Boolean relation between the properties of one or more information items.
DOM Document Object Model. The DOM provides an API to describe, access, create, and modify SGML-based documents, such as XML or HTML documents.
DTD Document Type Definition. DTDs define the valid content of an XML document.
Encoding The code system used for a given text. Code systems define a supported character set and the mapping of the characters onto a range of integers (character codes).
Entity In XML, entities are used for text substitution, for single characters as well as for document parts. In conceptual modeling, an entity is an abstract notion of an object that we want to include in a model.
Facet In XML Schema, a specific constraint defining or restricting the domain of a data type.
Foreign key A key (a property or combination of properties) that can be used to refer to external information items. See also Primary key.
Information set The abstract description of XML document contents, independent of syntax.
Instance An individual of a certain class or type.
Internet The largest network in the world. The Internet features a three-level hierarchy consisting of backbone networks, midlevel networks, and stub networks. It spans many different physical networks around the world with various protocols, including the Internet Protocol TCP/IP.
Kleene star An operation that produces the set of all possible concatenations of symbols from a given set, including the empty string.
Lexical space In XML Schema, the lexical space of a data type is defined by the set of character strings required to represent all values of this data type. Each value may have several representations within the lexical space; one specific representation is designated as the canonical form.
Markup Syntactical means to make text more readable or to add meta-information to a text. In English prose, markup consists of punctuation, parentheses, dashes, footnotes, and so on. In XML, markup consists of tags.
Mediation A process that allows diverse software systems to interoperate. Mediation implies syntactical and semantic conversion. See also Ontology.
Namespace A concept to uniquely separate a set of identifiers from other identifiers. Namespaces are used to avoid name clashes. In XML, namespaces are identified by means of a unique URI.
Nil value In XML a nil value is an artificial value indicating that a given element does not have a value. However, a nilled element may own attributes.
Nondeterminism Feature of the p-calculus to describe the situation that the receiver of a communication when two or more processes “compete” for it cannot be predetermined. The process system evolves differently depending on who makes the race.
Normalized string A character string is normalized by reducing whitespace within the string to a single whitespace character and by removing any whitespace from the beginning and end of the string.
Null value In object-oriented programming and SQL, a null value is an artificial value indicating that a certain variable or column does not have a value.
Object Constraint Language (OCL) A language defining constraints, pre- and postconditions, and navigation within UML diagrams.
Object-oriented programming A mainstream programming technique whereby data is encapsulated into object instances and can be accessed via the methods defined for a given object class.
Ontology An agreement about a shared conceptualization. Complete ontologies consist of vocabularies, thesauri, constraints, and axioms.
Parser A program that breaks a text string into a series of tokens, labeling each token with its grammatical role. XML parsers usually require that a document be well formed. Validating parsers can check a document instance against its schema definition.
Primary key A unique key (a property or combination of properties) that can be used to identify an information item. See also Foreign key.
Regular expression An expression describing a regular set.
Regular set A set of symbol strings is called regular if it can be obtained from a given alphabet of symbols with a finite number of concatenations, unions, and Kleene star operations.
Relational algebra Used to model the data stored in relational databases and queries defined on the data. The main relational functions are the set functions like union, intersection, and Cartesian product, plus selection (keeping only some rows) and projection (keeping only some columns). Relational algebra was developed by E. F. Codd.
Relational database management system (RDBMS) A database system based on the relational data model. Queries in relational databases are formulated with SQL.
Relax NG An alternate schema definition language, issued by the Organization for the Advancement of Structured Information Standards (OASIS).
SAX Simple API for XML. An API that provides methods for parsing XML documents (see Parser) and for retrieving elements.
Schema A definition that defines syntactic and semantic constraints of a certain class of information items.
SGML Standard Generalized Markup Language. A generic language for representing documents. SGML is defined in ISO 8879:1986.
SQL Structured Query Language. SQL is used as an interface to relational database management systems (RDBMSs). A series of standards by ISO and ANSI culminated in SQL-99 (SQL-3). While the original implementation of SQL in 1986 only supported flat tables, SQL-99 strives to provide relational support for complex objects. Currently, most RDBMSs support SQL-92.
Tag A syntactical means to mark up text. In XML, tags are enclosed in angled brackets and can own attributes.
Ternary association, ternary relationship A relationship between three information items.
Transformation The process of translating an XML document into a different—XML or non-XML—document, for example, for presentation purposes. Transformation may include changes in the structure, the vocabulary, the content, and the encoding of a document. Popular transformation engines are XSLT processors.
Unicode A 16-bit character set standard. Unicode covers all major modern written languages.
URI Universal Resource Identifier. A URI uniquely identifies a resource (typically a resource on the Internet) with a short string. URIs are defined in http://www.w3.org/hypertext/WWW/Addressing/URL/URI_Overview.html. The most common kind of URIs are URLs.
URL Uniform Resource Locator. A URL specifies the address of an Internet resource, such as a web page, an image, a sound file, or a script. URLs consist of a transfer protocol specification, such as http: or ftp:, a domain name, such as www.w3.org, and a path specification, such as http://www.w3.org/hypertext/WWW/Addressing/URL/.
View An interface to an information item or a set of information items, exposing only a limited property set.
W3C World Wide Web Consortium. A nonprofit organization responsible for the development of World Wide Web standards (recommendations).
Well formed An XML document is well formed if it complies with the syntax constraints defined in the XML 1.0 Recommendation.
Whitespace Any character that does not ink the paper when printed, for example: blank, newline, tab.
XML Extensible Markup Language. As a “slimmed-down” version of SGML, XML became a W3C recommendation in 1998. The XML V1.0 Recommendation specifies the syntax of well-formed documents and how document classes can be defined with a DTD.
XML Schema A W3C recommendation since May 2001, XML Schema introduces a hierarchy of built-in and user-defined data types, namespace support, and advanced facilities for structure definition and modularization of schemata, thus offering an alternative to schema definition with DTDs.
XPath The W3C recommendation for XPath defines the syntax and semantics of access operators to XML document nodes.
XQuery The W3C Working Draft for XQuery defines the syntax and semantics of an XML query language. XQuery is based on XPath V2.0.
XSLT The W3C recommendation for the Extensible Stylesheet Language (Transformations) defines the syntax and semantics of template-based document transformation. XSLT is based on XPath.