What is a markup language for documents, containing structured information?

20.5 Extensible markup language (XML)

Embedding mark-up in a document is not a new idea. Proofreaders refer to marking up a document in order to indicate the changes that are to be made. Using a precise set of symbols makes the interpretation of the proofreaders instructions much easier. Early word processing languages made extensive use of mark-up to define how the document was to be laid out. Markup became an expression that entered into almost everyone's (non-formal) vocabulary with the introduction of Hypertext Markup Language (HTML) which allowed easy exchange of document information over the Internet which could be displayed by browsers specially built to interpret HTML.

eXtensible Markup Language (XML) is a meta-language, a tool for defining markup languages using tags enclosed in angle brackets < … > to start an element of the language and < /… > to close an element. The elements may have properties, called attributes, and child elements. The main reasons for the importance of the development of XML is:

XML is a tool for defining markup languages.

XML languages can be used to develop standards for the interchange of data.

There are many XML parsers available which will check an XML document for well-formedness and validity.

The structure of XML lends itself easily to a tree representation – showing the derivation tree of the document.

An XML document has an associated definition of the allowed elements, element embeddings, that is, the possible parent-child relationships, and attributes. This is called a document type definition (DTD). The parser can check any XML document in two possible ways, either simply for well-formedness or it can also validate it against its DTD. A well-formed document must follow the general rules for any XML document whereas a valid document must also agree with the constraints defined in its DTD. We give an example here of a well-formed document and not concern ourselves at present with the structure of a DTD.

We might want to represent the following information about books: Publisher, Title, Author, ISBN, Category. As all books have a publisher then we could say that a book is a child of the publisher. In this case, we could represent some information in the following XML fragment.

This fragment would constitute a well-formed XML document. We have indented it so it is clear the structure of document. We can see it as a tree displayed with the root of the tree on the left-hand side –this is pictured in Figure 20.4.

Publisher Summary

Extensible Markup Language (XML) is an important data management tool. XML documents are text files marked with tags indicating the structure of the content of the files. XML is software and platform independent—i.e., it provides an excellent environment for transferring data between database systems. XML has been accepted by the World Wide Web Consortium (W3C) and has become a de facto standard for cross-platform data transfers. Because it is an open source specification, a number of application programming languages have been built on top of it, such as XHTML, RSS, MathML, GraphML, Scalable Vector Graphics, and MusicXML. Major database management systems (DBMSs) handle XML in two ways. Some store XML documents as binary objects. The documents are not searchable and therefore maybe accompanied by keywords assigned to the documents for search purposes. The documents are stored and retrieved as complete units. Other DBMSs store XML data in standard character columns and then generate complete documents for output. Although incorporating XML still is not a typical relational DBMS activity, its use is expanding.

XML and knowledge management

Extensible markup language (XML) is a fundamental enabling technology for content management and application integration. XML is a set of rules for defining data structures and thus making it possible for key elements in a document to be characterized according to meaning. It enables us to build a structure around the document’s attributes, and RDF (resource description framework) allows us to improve search mechanisms using the semantics of annotations (Decker et al., 2000). RDF uses a simple data model for representing properties of resources such as images, documents, and the relationships between them. The content of documents can be described using semantic annotations, which can then be used in searching for documents with certain content. RDF provides many advantages, such as: (1) a standard way to represent semantics, (2) supporting human readable and machine processable vocabularies, (3) standardized vocabularies within a particular community, and (4) eliminating the need for a centralized registry. Thus, RDF provides an information architecture that can extend capabilities for networking resources and information retrieval. XML makes it possible to deliver information to agents in a form that allows automatic processing after receipt and therefore distribute the processing load over a federation of agents that work cooperatively in problem solving.

VIII.B. XML in E-mail

Extensible markup language (XML) is taking the technology world by storm. It provides a simple way for exchanging structured data between applications within an organization, and external to it. This is a revolutionary concept within the IS world, and addresses key problems that have been experienced for many years. An XML document follows a structured layout as specified by a certain XML document definition, and the receiving application knows how to interpret the XML code and do something intelligent with it. Some e-mail vendors, both established and new entrants, are working toward the use of XML within e-mail.

XML in e-mail will provide two benefits. First, it will allow messages to intelligently handle themselves without user intervention. This will obviously only apply to some messages, as a good proportion of messages require personal review. E-mails that confirm meetings, announce flight delays, or provide time-limited information can automatically update the users schedule, notify them by pager of the flight delay, and delete themselves when the relevant time has passed.

The second area of benefit relates to integration with mobile and wireless devices. The display capabilities on such devices are vastly inferior to a desktop or laptop computer. Hence, an e-mail with XML tags will provide specific instructions to the device on how to appropriately display and format the content.

E-mail messages that can automatically initiate actions within an e-mail client and infrastructure hold the potential for great harm. For example, this would be an ideal way to transfer viruses or other damaging payloads between applications. Hence, vendors offering scanning and protection utilities will need to increase their capabilities to prevent against such negative occurrences.

Introduction

Extensible Markup Language, or XML, has met with immense popularity with the continually increasing need for dispersed systems to communicate in a growingly connected environment. Developed in 1996 and recorded by the World Wide Web Consortium (W3C) in 1998, XML offers many advantages over complex and proprietary approaches to communication. True to its name of extensible, XML documents can be as simple as a single set of elements or as complex as necessary to accomplish nearly any task. Microsoft continues to make fundamental shifts in its technology architecture to support the processing, delivery, and use of XML, and many other organizations are quickly adopting it as an integral part of their solutions. With industry-standard support, extensible structure, and a low learning curve, XML will continue to increase its role and impact on technology solutions.

As one of the more publicized additions to SQL Server 2000, native XML support allows your organization to begin taking advantage of XML and prepare your applications for its increased use in the future. The addition of the FOR XML statement in T-SQL offers the straightforward delivery of XML-formatted result sets. Several new stored procedures are available for using XML documents as record sets in T-SQL. Client applications can take advantage of XML using the new extensions to ActiveX Data Objects (ADO) in version 2.6. SQL Server 2000’s support of HTTP access allows remote applications to retrieve and manipulate SQL Server data as XML over the Internet, with very little additional configuration.

This chapter provides an overview of XML, its components, and its structure. You will configure support for HTTP server access using IIS and query SQL Server using a Web browser. Advanced XML topics such as XPath statements and XML views will introduce you to real-world XML solutions and walk you through creating the necessary components to utilize XML in client and server applications.

Data Exchange

Service units don't do anything without exchanging data to submit and accept requests, return results, and potentially collaborate, receive event notices, or issue event notices. Shared services exchange data with multiple users.

Data exchanged with a service unit must be consistent for all users so that the service deals with all requests in the same way. The data models of records exchanged should be subsets of the ELDM. These subsets are often called views because they represent that subset of the ELDM data elements that is viewed by the participants in the exchange for the particular subject matter. This is similar to a display or a report that shows selected data elements from a database.

The data exchanged among service units are generally communicated by automated business processes. Requests to a service unit should be received by a business process and results should be returned by a business process. Requests for status of a process as well as receipt and publication of event notices involve exchange of data with business processes. Electronic business documents are created and managed by business processes and must be archived for future reference. Though some service units may have their business processes embedded in applications, it is important to understand that, for the most part, the exchanges of data between service units are essentially exchanges between business processes within the service units.

eXtensible Markup Language (XML) was recognized fairly early in the 1990s as a useful form of data interchange. It has several important characteristics:

XML documents (i.e., records) are somewhat self-documenting. Each element is tagged with a descriptive name.

The fields are variable in length, with special characters designating the beginning and ending so that the format remains valid, even if the length of a field changes, and text fields can take whatever space is required.

A receiving program can select fields of interest based on the tags and ignore any other fields that may have been added by the sender, so the receiver can continue to use documents that have been expanded for other purposes.

XML is used to specify the structure of XML documents (using XML Schema) so that shared specifications can be used for computational validation.

XML is also used to express the transformation of XML documents by using Extensible Stylesheet Language Transformations (XSLT) so that there is a standard, computer-interpreted language for document transformation.

XML is independent of the computing platform and computer languages used to send or receive it, so there is compatibility between diverse sending and receiving technologies.

XML can be exchanged using HTTP and HTTPS, protocols of the World Wide Web, so that existing ports are compatible and the data can pass through existing firewalls.

A widely accepted standard for electronic signatures is based on XML. Standards for encryption and signatures for XML documents are discussed in Chapter 6.

XML, along with XML Schema, XSLT, HTTP, HTTPS, and related standards, has been developed by the World Wide Web Consortium (W3C). Though other forms such as electronic data interchange (EDI) are still widely used, XML has emerged as the preferred form for exchanging electronic documents between systems and enterprises. The flexibility of XML is a trade-off with the verbosity that increases communication overhead.

An example use of XML follows. This XML document is structured to contain a collection of customer orders—in the example there is only one order:

     100-watt speaker, Mahogany case

     2

     235.95

     CD Player, Mahogany case

     1

     167.95

The XML expressions are indented for readability. Each expression begins with to identify the data element (where name is the name of the data element) and ends with (a slash prefix) to specify the end of the data element. An element may contain a primitive value (that is, a data type that is not defined in terms of other data types), another element, or multiple elements. A primitive element may be expressed with both a name and value together, for example the Product element in the example, by ending the value segment with />, and other attributes can be expressed with the name such as at the beginning of the Order element in the example. could contain multiple orders, but in this case only one order is shown, which starts with and ends with . Within the Order are elements for Customer and Order Items. The Customer element only specifies the customer ID. There are then two order items, each containing several order-item attributes. XML structures are specified with a specialized XML language called XML Schema so the format can be validated by a generalized computer program.

Application adapters provided by integration middleware should provide for transformation between the application internal representation of data and an appropriate XML representation.

Is a markup language for web documents containing structured information including words and pictures?

Is a markup language designed to describe data?

Which of the following is a markup language?

Which of the following is a markup language for defining the visual design of a web page or group of pages?