A Technical Introduction to XMLA Technical Introduction to XMLOctober 3, 1. Norman Walsh. Author's Note: It is somewhat remarkable to think that this article, which appeared. Winter 1. 99. 7 edition of the World Wide Web Journal was out of date. XML Recommendation was approved. February. And even as this update brings the article back into line with the final. When finished, these. This introduction to XML presents the Extensible Markup Language at a reasonably technical. In addition. to. covering the XML 1. Specification, this article outlines related XML specifications. DriveImage XML is an easy to use and reliable program for imaging and backing up partitions and logical drives. The program allows you to: Backup logical drives and. Download the latest version of RealPlayer with RealTimes and get the latest features! I'm generating some xml files that needs to conform to an xsd file that was given to me. What's the best way to verify they conform? Cooktop is an editor and development environment for XML, DTD, and XSLT documents; Cooktop is a Windows application; Best of all, it's free! XML Notepad 2007 provides a simple intuitive user interface for browsing and editing XML documents. Download file when clicking on the link (instead of navigating to the file). The article is organized in four main sections plus an appendix. Almost all documents have some structure. The XML. specification defines a standard way to add markup to documents. These include. vector graphics, e- commerce transactions, mathematical equations, object meta- data. APIs, and a thousand other kinds of structured information. In HTML, both the tag semantics and the tag set are fixed. An < h. 1> is. However, these changes. And for people who want to disseminate information widely. Netscape and Internet Explorer are. In fact XML is really a meta- language. In other words, XML provides a facility to define tags. Uniform Type Identifier (UTI) public.xml: UTI conformation: public.text: Developed by: World Wide Web Consortium: Type of format: Markup language: Extended from. XML is a markup language. The mighty ones who created this acronym cheated a little, as XML stands for eXtensible Markup Language. HTML.it: corsi, guide, articoli e script per webmaster e webdesigner, gli approfondimenti necessari sui trend del design e della programmazione. ![]() ![]() Since there's no predefined tag set, there. All of the semantics of an XML document will either be. XML is defined as an application profile of SGML. SGML is. the. Standard Generalized Markup Language defined by ISO 8. SGML has been the standard. Defining XML as an application. SGML means that any fully conformant SGML system will be able to read XML documents. XML is, roughly speaking, a. SGML. In particular, treatment of white space immediately adjacent to. XML. was. created so that richly structured documents could be used over the web. The only viable. alternatives, HTML and SGML, are not practical for this purpose. Full SGML systems solve large, complex problems that justify their expense. While XML. is being. SGML a more satisfactory solution for the creation and long- time. In many organizations, filtering SGML to XML will be. If you are. interested in more technical detail about a particular topic, please consult the. It shall be straightforward to use XML over the Internet. Users must be able to view. XML. documents as quickly and easily as HTML documents. In practice, this will only be. XML browsers are as robust and widely available as HTML browsers, but the principle. XML should be beneficial to a wide. Although. the. initial focus is on serving structured documents over the web, it is not meant to. XML. Most of the people involved in the XML effort come. SGML. XML was designed pragmatically, to be compatible with existing standards while. The colloquial way. XML documents. Optional features inevitably raise compatibility problems when users want to. If you don't have an XML. XML from somewhere, you ought to be able to. Standards efforts are notoriously slow. In many ways a corollary to rule 4. XML must be expressed in EBNF and must be amenable to modern. There are a number of technical reasons why the SGML. EBNF. Writing a proper SGML parser requires handling a variety of rarely used and. Although there will eventually be sophisticated. XML content, they won't appear immediately. In the interim. it. XML documents in other ways: directly in a text editor. Perl scripts, etc. Several SGML language features were. SGML documents. From an abstract point of view, these documents. SGML parser (or the person writing it, anyway). The XML specification is the primary focus of this. In addition to simple. HTML's < A> tag, XML has mechanisms for links between multiple. XPointer describes how to address. XLink describes how to associate two or more resources. Please consult the discussion of EBNF in the appendix of this article for a. A simple. XML. document is presented in Example. A Simple XML Document< ? This is. the XML declaration . While it is not required, its presence explicitly identifies the document as. XML document and indicates the version of XML to which it was authored. Unlike SGML, XML does not require a document. However, a document type declaration can be supplied, and some documents. While most elements. HTML's < hr> tag, for example, or a. Doc. Book's. < xref> tag). The trailing /> in the modified syntax indicates to a. XML document that the element is empty and no matching end- tag. Since XML documents do not require a document type declaration. XML parser to determine which tags were. XML has softened the. EMPTY and elements which. In XML, it is legal to use the empty- element tag syntax in. It's also legal to use a start- tag/end- tag pair for empty elements. If interoperability is of any concern, it's. EMPTY. and to only use the empty- element tag form for those elements. There are six kinds of markup that. XML document: elements, entity references, comments, processing instructions. The following sections introduce. Delimited by angle brackets, most elements. Some elements may be empty, as seen. If an element is not empty, it begins with a start- tag. In XML, all attribute values must be quoted. The left angle bracket, < , for instance, identifies. In order to insert these characters into. In XML, entities. Entities are also used to refer to. Defining your own entity names is discussed. In. order to use an entity, you simply reference it by name. Entity references begin with. So the string. < element> can be represented in an XML document as. This is a mechanism for inserting. Both of these refer to character number. U+2. 11. E from Unicode (which is the standard Rx prescription symbol, in case you were. Comments can contain any. You can place comments between markup anywhere. An XML processor. The name, called the. PI target, identifies the PI to the application. Applications should process only. PIs. Any data that follows the PI target. The names used in. PIs may be. declared as notations in order to formally identify them. It might contain characters that. XML. parser would ordinarily recognize as markup (< and & , for example). Elements, entity references, comments, and processing instructions. If you have experience with SGML, you will recognize these declarations. SGML DTDs (Document Type Definitions). If you have never seen them before, their. Consider the old joke example introduced earlier. Would. this be. meaningful? It. just. doesn't mean anything. So, if the document is to have meaning, and certainly if you're writing. Declarations are where these constraints can be expressed. Meta- information includes the allowed sequence and nesting of tags. XML, the formats of some external (non- XML). A typical element. ELEMENT oldjoke (burns+, allen, applause?)>. This declaration identifies the element named oldjoke. Its content model. The content model defines what an element may contain. In. this. case, an oldjoke must contain burns and allen and may contain. The commas between element names indicate that they must occur in. The plus after burns indicates that it may be repeated more than once. The question mark after applause indicates that it is. A name with no punctuation. The moniker PCDATA stands for parseable character data . Elements that. contain both other elements and #PCDATA are said to have mixed content . All mixed. content models must have this form: #PCDATA must come first, all of the elements. The ANY content model is sometimes useful during document conversion, but. Element Declarations for Old Jokes< ! ELEMENT oldjoke (burns+, allen, applause?)>. ELEMENT burns (#PCDATA . A typical attribute. ATTLIST oldjoke. ID. CDATA. status ( funny . Don't confuse CDATA attributes. CDATA sections, they are. All of the ID values used. IDs uniquely identify individual elements in a document. The value of an IDREFS attribute may contain multiple IDREF values separated. The. value of an ENTITIES attribute may contain multiple entity names separated by white. In general, an NMTOKEN. The value of an NMTOKENS attribute may contain multiple NMTOKEN values. This is frequently called an enumerated type because each of the possible values. If a value. is not. XML processor must proceed without one. The attribute value is not. In this. case. the attribute is not required, but if it occurs, it must have the specified value. One use for fixed attributes. A complete discussion is beyond the scope. XLink specification. That construct. can be a chunk of regular text, a chunk of the document type declaration, or a reference. Typical Entity Declarations< ! ENTITY. ATI. . The first entity in Example 3 is an internal entity. Internal entities allow you to define shortcuts for frequently typed text. External entities allow an. XML document to refer to the contents of another file. External entities contain either. If they contain text, the content of the external file is inserted. Binary data is. not. Binary data is used to reference. XML content in the document. The XML. processor will parse the content of that file as if it occurred literally at that. The. ATIlogo entity can only be used as the value of an ENTITY (or ENTITIES). The XML processor will pass this. A parameter entity. The percent sign is also used in references to parameter entities. Parameter entity references are immediately expanded in. Parameter entities are not recognized in. In order to make more explicit the fact that these two elements. The advantage. of using a parameter entity is two- fold. First, it allows you to give a descriptive. ENTITY % personcontent . This information is passed to the. A typical notation. NOTATION GIF8. 7A SYSTEM . However. there are some instances where the declaration is required. Authoring Environments. Most authoring environments need to read and process document type declarations in. Without a DTD, there is no way for the. For more detail, see the. White Space Handling, later in this document. All XML documents must have a single root element that contains. Additional declarations may come from an external. DTD. called the external subset, or be included directly in the document, the internal. XML version=. In this case. XLink specification.
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