## 3 Markup languages
### Markup languages for web applications  
Another important development of markup languages is for applications on web services, such as resource description, ontologies, interoperability standards and so on. For examples, the Resource Description Framework (RDF) [33], the Web Ontology Language (OWL), Commerce XML (cXML), SOAP (Simple Object Access Protocol), WSDL (Web Service Description Language), and XML-RPC (Remote Procedure Calls) are the key contributors. RDF integrates a variety of applications from library catalogues and world-wide directories for the syndication and aggregation of news, software, and content to personal collections of music, photos, and events using XML as an interchange syntax [33]. As a lightweight ontology system, the RDF specifications support the exchange of knowledge on the Web. The OWL [34] is designed for use when the information contained in documents needs to be processed by applications, as opposed to situations where the information only needs to be presented to humans. As implied in its name, OWL can be used to explicitly represent \"ontology\", which consists of the meaning of terms in vocabularies and the relationships between those terms. cXML [35] is a well-defined, robust language designed for consistent communication of business documents between procurement applications, e-commerce hubs and suppliers. cXML is defined by a set of lightweight XML DTDs and its transactions consist of _documents_, which are simple text files containing values enclosed by predefined tags. SOAP defines the XML-based message format that Web service-enabled applications use to communicate and interoperate with each other over theWeb [36]. Based on SOAP, WDSL is a collection of metadata about XML-based services used to specify the procedures to discover functional and technical information about Web services over the Web [37]. XML-RPC is a remote procedure call protocol that uses XML to encode its calls and HTTP (Hypertext Transfer Protocol) as a transfer mechanism [38]. These XML-based standards enable applications to call functions from other applications, running on any hardware platform regardless of operating systems or programming languages, and have started finding their positions to play a central role in building and integrating enterprise applications. For instance, [PERSON] discusses the application of SOAP, WSDL together with UDDI (Universal Description, Discovery and Integration) to enterprise boundaries business-to-business (B2B) trade and outsourcing through application service providers (ASPs) [39]. Comparatively, [PERSON] argues that the traditional Web service triplets SOAP, WSDL and UDDI allow enterprise application integration and B2B integration only possible at syntactic level, and therefore advocates using XML-RPC to enable semantic level integration [40].  
Table 1 summarizes the core markup languages.  
\begin{table}
\begin{tabular}{l|c|l|l|l} \hline
**Language** & **Based on** & **Developer** & **Initial** & **Major applications** \\  & & & **release** & \\ \hline Generalized Mark-up Language (GML) & – & IBM & 1960s & Document \\ \hline Standard Generalized Mark-up Language (SGML) & GML & ISO & 1986 & Document \\ \hline HyperText Markup Language (HTML) & SGML & W3C \& WHATWG & 1991 & The World Wide Web \\ \hline \end{tabular}
\end{table}
Table 1: Summary of the core markup languages.