VIVA WEB TECHNOLOGIES Question & Answers
1.Q: After I have edited an HTML file, I cannot view the result in my browser. Why?
A: Make sure that you have saved the file with a proper name and extension like "c:\mypage.htm". Also make sure that you use the same name when you open the file in your browser.
A: Make sure that you have saved the file with a proper name and extension like "c:\mypage.htm". Also make sure that you use the same name when you open the file in your browser.
2.Q: I have edited an HTML file, but the changes don't show in the browser. Why?
A: A browser caches pages so it doesn't have to read the same page twice. When you have modified a page, the browser doesn't know that. Use the browser's refresh/reload button to force the browser to reload the page.
A: A browser caches pages so it doesn't have to read the same page twice. When you have modified a page, the browser doesn't know that. Use the browser's refresh/reload button to force the browser to reload the page.
3.Q: What browser should I use?
A: You can do all the training with all of the well-known browsers, like Internet Explorer, Firefox, Netscape, or Opera. However, some of the examples in our advanced classes require the latest versions of the browsers.
4.Q: Does my computer have to run Windows? What about a Mac?
A: You can do all your training on a non-Windows computer like a Mac.
A: You can do all your training on a non-Windows computer like a Mac.
1. What is XML?
(ans) XML is the Extensible Markup Language. It improves the functionality of the Web by letting you identify your information in a more accurate, flexible, and adaptable way.
It is extensible because it is not a fixed format like HTML (which is a single, predefined markup language). Instead, XML is actually a metalanguage—a language for describing other languages—which lets you design your own markup languages for limitless different types of documents. XML can do this because it's written in SGML, the international standard metalanguage for text document markup (ISO 8879).
2.What is a markup language?
(ans) A markup language is a set of words and symbols for describing the identity of pieces of a document (for example ‘this is a paragraph’, ‘this is a heading’, ‘this is a list’, ‘this is the caption of this figure’, etc). Programs can use this with a stylesheet to create output for screen, print, audio, video, Braille, etc.
Some markup languages (eg those used in wordprocessors) only describe appearances (‘this is italics’, ‘this is bold’), but this method can only be used for display, and is not normally re-usable for anything else.
XML is sometimes referred to as ‘self-describing data’ because the names of the markup elements should represent the type of content they hold.
3. What is XML for (aka ‘Where should I use XML’)?
(ans) Its goal is to enable generic SGML to be served, received, and processed on the Web in the way that is now possible with HTML. XML has been designed for ease of implementation and for interoperability with both SGML and HTML.
SeeWhere's the spec?
Despite early attempts, browsers never allowed other SGML, only HTML (although there were unknownplugins), and they allowed it (even encouraged it) to be corrupted or broken, which held development back for over a decade by making it impossible to program for it reliably. XML fixes that by making it compulsory to stick to the rules, and by making the rules much simpler than SGML.
But XML is not just for Web pages: in fact it's very rarely used for Web pages on its own because browsers still don't provide reliable support for formatting and transforming it. Common uses for XML include:
Information identification
because you can define your own markup, you can define meaningful names for all your information items.
Information storage
because XML is portable and non-proprietary, it can be used to store textual information across any platform. Because it is backed by an international standard, it will remain accessible and processable as a data format.
Information structure
XML can therefore be used to store and identify any kind of (hierarchical) information structure, especially for long, deep, or complex document sets or data sources, making it ideal for an information-management back-end to serving the Web. This is its most common Web application, with a transformation system to serve it as HTML until such time as browsers are able to handle XML consistently.
Publishing
The original goal of XML as defined in the quotation at the start of this section. Combining the three previous topics (identity, storage, structure) means it is possible to get all the benefits of robust document management and control (with XML) and publish to the Web (as HTML) as well as to paper (as PDF) and to other formats (eg Braille, Audio, etc) from a single source document by using the appropriate stylesheets.
Messaging and data transfer
XML is also very heavily used for enclosing or encapsulating information in order to pass it between different computing systems which would otherwise be unable to communicate. By providing a lingua franca for data identity and structure, it provides a common envelope for inter-process communication (messaging).
Web services
Building on all of these, as well as its use in browsers, machine-processable data can be exchanged between consenting systems, where before it was only comprehensible by humans (HTML). Weather services, e-commerce sites, blog newsfeeds, AJaX sites, and thousands of other data-exchange services use XML for data management and transmission, and the web browser for display and interaction.
4. What is SGML?
(ans)SGML is the Standard Generalized Markup Language (ISO 8879:1986), the international standard for defining descriptions of the structure of different types of electronic document. There is an SGML FAQ from David Megginson athttp://math.albany.edu:8800/hm/sgml/cts-faq.htm
SGML is very large, powerful, and complex. It has been in heavy industrial and commercial use for nearly two decades, and there is a significant body of expertise and software to go with it.
XML is a lightweight cut-down version of SGML which keeps enough of its functionality to make it useful but removes all the optional features which made SGML too complex to program for in a Web environment.
5. What is HTML?
(ANS)HTML is the HyperText Markup Language (RFC 1866), which started as a small application of question A.4, SGML for the Web, originating with Tim Berners-Lee at CERN in 1989–90.
It defines a very simple class of report-style documents, with section headings, paragraphs, lists, tables, and illustrations, with a few informational elements, but very few presentational elements [10], plus some hypertext and multimedia. See the question on extending HTML. The current recommendation is to use the XML version, XHTML. There is a HTML and XHTML FAQ maintained by Steven Pemberton at http://www.w3.org/MarkUp/2004/xhtml-faq
6.Aren't XML, SGML, and HTML all the same thing?
(ans) Not quite; SGML is the mother tongue, and has been used for describing thousands of different document types in many fields of human activity, from transcriptions of ancient Irish manuscripts to the technical documentation for stealth bombers, and from patients' medical and clinical records to musical notation. SGML is very large and complex, however, and probably overkill for most common office desktop applications.
XML is an abbreviated version of SGML, to make it easier to use over the Web, easier for you to define your own document types, and easier for programmers to write programs to handle them. It omits all the complex and less-used options of SGML in return for the benefits of being easier to write applications for, easier to understand, and more suited to delivery and interoperability over the Web. But it is still SGML, and XML files may still be processed in the same way as any other SGML file (see the question on XML software).
HTML is just one of many SGML or XML applications—the one most frequently used on the Web.
Technical readers will find it more useful to think of XML as being SGML−− rather than HTML++.
7.Who is responsible for XML?
(ans) XML is a project of the World Wide Web Consortium (W3C), and the development of the specification is supervised by an XML Working Group. A Special Interest Group of co-opted contributors and experts from various fields contributed comments and reviews by email.
XML is a public format: it is not a proprietary development of any company, although the membership of the WG and the SIG represented companies as well as research and academic institutions. The v1.0 specification was accepted by the W3C as a Recommendation on Feb 10, 1998.
8.Why is XML such an important development?
(Ans) It removes two constraints which were holding back Web developments:
dependence on a single, inflexible document type (HTML) which was being much abused for tasks it was never designed for;
the complexity of full question A.4, SGML, whose syntax allows many powerful but hard-to-program options.
XML allows the flexible development of user-defined document types. It provides a robust, non-proprietary, persistent, and verifiable file format for the storage and transmission of text and data both on and off the Web; and it removes the more complex options of SGML, making it easier to program for.
9.Why not just carry on extending HTML?
(ans) HTML was already overburdened with dozens of interesting but incompatible inventions from different manufacturers, because it provides only one way of describing your information.
XML allows groups of people or organizations to question C.13, create their own customized markup applications for exchanging information in their domain (music, chemistry, electronics, hill-walking, finance, surfing, petroleum geology, linguistics, cooking, knitting, stellar cartography, history, engineering, rabbit-keeping, question C.19, mathematics, genealogy, etc).
HTML is now well beyond the limit of its usefulness as a way of describing information, and while it will continue to play an important role for the content it currently represents, many new applications require a more robust and flexible infrastructure.
10.Why should I use XML? (aka ‘What is XML for?)
(ans) Here are a few reasons for using XML (in no particular order). Not all of these will apply to your own requirements, and you may have additional reasons not mentioned here (if so, please let the editor of the FAQ know!).
· XML can be used to describe and identify information accurately and unambiguously, in a way that computers can be programmed to ‘understand’ your information (well, at least manipulate as if they could understand it).
· XML allows documents which are all the same type to be created and handled consistently and without structural errors, because it provides a standardised way of describing, controlling, or allowing/disallowing particular types of document structure. [Note that this has absolutely nothing whatever to do with formatting, appearance, or the actual text or data content of your documents, only the structure of them. If you want styling or formatting, see question C.24, ‘How do I control formatting and appearance?’.]
· XML provides a robust and durable format for information storage and transmission. Robust because it is based on a proven standard, and can thus be tested and verified; durable (persistent) because it uses plain-text file formats which will outlast proprietary binary ones.
· XML provides a common syntax for messaging systems for the exchange of information between applications. Previously, each messaging system had its own format and all were different, which made inter-system messaging unnecessarily messy, complex, and expensive. If everyone uses the same syntax it makes writing these systems much faster and more reliable.
· XML is free. Not just free of charge (free as in beer) but free of legal encumbrances (free as in speech). It doesn't belong to anyone, so it can't be hijacked or pirated. And you don't have to pay a fee to use it (you can of course choose to use commercial software to deal with it, for lots of good reasons, but you don't pay for XML itself).
· XML information can be manipulated programmatically (under machine control), so XML documents can be pieced together from disparate sources, or taken apart and re-used in different ways. They can be converted into any other format with no loss of information.
· XML lets you separate form (appearance) from content. Your XML file contains your document information (text, data) and identifies its structure: your formatting and other processing needs are identified separately in a stylesheet or processing system. The two are combined at output time to apply the required formatting to the text or data identified by its structure (location, position, rank, order, or whatever).
· Any of the Design Goals listed in the XML Specification.
11. Where do I find more information about XML?
(ans) Online, there's the XML Specification and the ancillary documentation available from theW3C; Robin Cover's SGML/XML Web pages with an extensive list of online reference material and links to software; and a summary and condensed FAQFPRIVATE Google or other search engine.
For offline resources, see the lists of books, articles, and software for XML in Robin Cover'sSGML and XML Web pages. That site should always be your first port of call.
The events listed below are the ones I have been told about. Please mail me if you come across others: there are many other XML events around the world, and most of them are announced on the mailing lists and newsgroups.
12.Where can I discuss implementation and development of XML?
(Ans) The two principal online support media are Usenet newsgroups and mailing lists. The IRC network is also used to some extent, and most individual projects and programs have their own topic-specific bulletin-boards on their web sites.
For off-line support, see question A.11, ‘Where do I find more information about XML?’ for details of conferences and summerschools.
· The Usenet newsgroups are comp.text.xml and to a certain extent comp.text.sgml. Ask your Internet Provider for access to these, or use a Web interface like Google Groups. If your browser or mailer doesn't provide newsreading facilities, install one that does, or (better) use a standalone newsreader.
· The general-purpose mailing list for public discussion is XML-L: to subscribe, visit the Web site and click on the link to join.
· For those developing software components for XML there is the xml-dev mailing list. You can subscribe by sending a 1–line mail message to xml-dev-request@lists.xml.org saying just SUBSCRIBE. Note that this list is for those people actively involved in developing resources for XML. It is not for general information about XML (use the XML-L list above for that).
· The XSL-List is for for discussing XSL (both XSLT and XSL:FO). For details of how to subscribe, see http://www.mulberrytech.com/xsl/xsl-list.
13. What is the difference between XML and C or C++ or Java?
(ans) C and C++ (and other languages like FORTRAN, or Pascal, or Visual Basic, or Java or hundreds more) are programming languages with which you specify calculations, actions, and decisions to be carried out in order:
mod curconfig[if left(date,6) = "01-Apr",
t.put "April Fool!",
f.put days('31102005','DDMMYYYY') -
days(sdate,'DDMMYYYY')
" more shopping days to Samhain"];
XML is a markup specification language with which you can design ways of describing information (text or data), usually for storage, transmission, or processing by a program. It says nothing about what you should do with the data (although your choice of element names may hint at what they are for):
<part num="DA42" models="LS AR DF HG KJ"
update="2001-11-22">
<name>Camshaft end bearing retention circlip</name>
<image drawing="RR98-dh37" type="SVG" x="476"
y="226"/>
<maker id="RQ778">Ringtown Fasteners Ltd</maker>
<notes>Angle-nosed insertion tool <tool
id="GH25"/> is required for the removal
and replacement of this part.</notes>
</part>
On its own, an SGML or XML file (including HTML) doesn't do anything. It's a data format which just sits there until you run a program which does something with it. See also the question about how to run or execute XML files.
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