Blogger blogs use XML, and Tumblr blogs use HTML, but they both do the same thing. What is the difference between XML and HTML and what are the pros and cons of using them?
HTML is a markup language for describing hypertext ("with links") documents.
XML is a generic markup language designed for using as a base for building custom markup languages.
They are different tools for different jobs.
When you write a template for either Blogger or Tumblr, you are using a template language. Blogger's template language happens to be built in XML. The template language is combined with your data to generate the HTML documents that are sent to the browser.
XML was developed to describe data and to focalize on what the data represent.
HTML was developed to display data about to focalize on the way that data looks.
HTML is about displaying data, XML is about describing information.
Reference
In an ideal world, HTML would be just one of many XML vocabularies. The only reason it isn't is history: (a) it was wild on the web before XML was formulated, and (b) it developed a culture where you could write any old garbage and the browsers would try and make sense of it, whereas XML insisted that you stick to the rules.
The W3C spent about ten years trying to make this vision happen, through the medium of XHTML, but in the end the browser vendors decided to go their own way.
XML was developed to describe data and to focalize on what the data represents.
Whereas HTML describes the structure of Web pages using markup.
In other words, HTML is used to display data, XML is used to store and transport data.
Related
While I am trying to understand what semantic web is and what technologies are used, I saw from https://en.wikipedia.org/wiki/Semantic_Web#Semantic_Web_solutions
The Semantic Web takes the solution further. It involves publishing in
languages specifically designed for data: Resource Description
Framework (RDF), Web Ontology Language (OWL), and Extensible Markup
Language (XML). HTML describes documents and the links between them.
RDF, OWL, and XML, by contrast, can describe arbitrary things such as
people, meetings, or airplane parts.
In Semantic web,
is HTML not used at all, and is XML used instead?
Is the principle of separation of semantics (content) from presentation in HTML not related to semantic web?
Is JSON not used and is XML used instead?
JSON is overwhelmingly used for representing data than XML, and if semantic web uses XML, does it mean that semantic web is not a trend?
In related tags to semantic web, I find more HTML tag than XML tag, and can't find JSON tag.
RDF is conceptually a graph database with OWL providing logic features (axioms for extending a ground RDF graph with additional induced tuples such as for transitivity). RDF has per se nothing to do with markup (XML, SGML, HTML) but RDF/XML is one of several standardized serialization formats for an RDF graph, another one being turtle/N3.
However, RDF was specifically introduced to represent semantic data on the Web. Hence, there are additional serialization formats for RDF graphs in Web documents: RDFa for embedding RDF data in HTML or XML documents, and JSON-LD as a JSON format for serializing RDF graphs (with a focus on linked data).
The term "semantic web" refers primarily to a concept, rather than a particular implementation of that concept.
Over time, various standards have been developed and implemented with the aim of implementing the concept, and in particular the W3C has a long-running project to create a stack of such standards covering the requirements they see for a successful semantic web. The W3C tries to build standards on top of each other, and sees XML as the base on which much of the rest of their work is based, so their definitions often use an XML syntax.
In practice, though, HTML is overwhelmingly the language of the web, and XHTML (an attempt to re-specify HTML as an XML-based standard) is considered to have failed. As such, HTML-based technologies such as "microformats" (metadata embedded in HTML via specific patterns of markup) are a popular alternative to more strictly machine-oriented XML formats, and are often designed to interact with them.
Similarly, JSON became popular as a light-weight data interchange format without the perceived complexity of XML and XML-based document standards. Over time, tools have been built to formalise and work with JSON, some of which may well be involved in "semantic web" concepts.
I think an important distinction is between the low-level markup format of data - XML, HTML, JSON - and the higher-level technologies being implemented. For instance, RDF can be written in various "concrete syntaxes"; one of those is an XML-based markup, but others are designed to be "human-readable" (Turtle/N3), embedded in HTML (RDFa) or combined into a JSON format (JSON-LD). The same is true of other standards, such as OWL. It is therefore somewhat misleading to think about "using XML instead of HTML or JSON"; the real distinction might be more like "using an Ontology definition rather than a document template".
I am using HTML to make a websites. I know an alternative languages to markup a website: XHTML, WML. Is there any more markup languages? Can I make a website only with XML or SGML?
Thank you for responses.
There aren't many.
To have a browser make your website viewable, you must provide your website in some language your browser can understand. Just plaintext and HTML work universally, there is quite some SVG and PDF support these days, but the only language you can use that can do all the things most people want a website to be able to do, you will have to use HTML or XHTML in some way. Either through JS or by some templating system, but you'll have to use it to generate what's commonly accepted as being a webpage as far as I'm aware.
That being said, there are some languages like Haml, which can be 'compiled' to HTML so you could use that instead. There are also converters for other XML-based languages and such.
If you want to deliver XML from your server, you can convert it to HTML in the browser using either
(a) XSLT 1.0: nearly all browsers have built in support for XSLT 1.0, which can be invoked using the xml-stylesheet processing instruction embedded in the XML
(b) XSLT 3.0: supported using Saxon-JS, which can be invoked using a small Javascript call in a skeletal HTML page.
(c) CSS: if the XML is reasonably close in structure to what you want to present to the user, you can attach styling properties to the XML elements using CSS.
You can also of course maintain your content in XML and convert it to rendered HTML using XSLT either at publishing time, or when each page is requested using code on the server to do the conversion on demand.
Many scientific journals use XML (actually JATS XML) for publishing scientific articles. XML in this case is transforming to HTML either on server or on client side by javascript. As example you can look here, where taking place client-side transformation. But Google will not index such XML.
The content tends to be mixed with it's form when expressed as a HTML+CSS+JS document. Almost every modern website requires CSS and/or JavaScript to be readable. Most of them are not easy to parse automatically because they relay on web browser to render it. Sections of the document are defined using visual clues, colors and formatting. One can use HTML5 tags like <article> but those are not a part of any bigger structure as far as I know, and still can contain non-content elements.
Websites are basically apps or clients.
Is there any standard that can be used to serve content of a website that has a well defined schema? An API for websites that could be used to express content in the form that is easy to server, parse, store, cryptographically sign...
I'm aware of formats like XML and JSON but I have not managed to find any standardized way to express a blog post as a JSON document.
An example of what I have in mind:
This question can be fetched as an JSON document using Stackexchange API. The result is machine readable and easy to parse but is in not standardized. It reflects details of Stackexchange specific data structures. Other QA website will have different API, with different structure and formats even though both have questions and answers.
There are two important standards out there dealing with the semantic aspect of a web page, like the one you are looking for. Microdata and RDFa. With their aid, you can pick a certain open vocabulary to describe your data or create your own based on them.
With JSON-LD also, you can create a schema for JSON documents like the XML schema is for the XML documents.
So, yeah, is HTML a particular application of XML? Like, instead of user-customizable tags, "hard coded" fixed tags decided by the W3C and interpreted by navigators? Or are them totally different things?
Also, in which case is XML better than a database to transfer information inside a Web application? (I was thinking, saving users information or things like that may do better with XML documents than with a database).
Here's a history of HTML
...The HTML that Tim invented was strongly based on SGML (Standard Generalized Mark-up Language), an internationally agreed upon method for marking up text into structural units such as paragraphs, headings, list items and so on. SGML could be implemented on any machine. The idea was that the language was independent of the formatter (the browser or other viewing software) which actually displayed the text on the screen. The use of pairs of tags such as and is taken directly from SGML, which does exactly the same. The SGML elements used in Tim's HTML included P (paragraph); H1 through H6 (heading level 1 through heading level 6); OL (ordered lists); UL (unordered lists); LI (list items) and various others. What SGML does not include, of course, are hypertext links: the idea of using the anchor element with the HREF attribute was purely Tim's invention, as was the now-famous `www.name.name' format for addressing machines on the Web....
And in no case is XML "better" than a database (are cakes better than ovens?). XML isn't for storing data, it's for transfering it. Unless the data is absolutely minimal, you have to find some other way to store it. Opening static XML files on the file system over and over as you save and read data is a terrible way to go about it.
So, yeah, is HTML a particular application of XML?
No.
HTML 4 is an application of SGML, but most parsers for it do not treat it as such.
XHTML is an application of XML, but it is usually served as text/html instead of application/xhtml+xml and so is treated like HTML.
HTML 5 is not an application of either SGML or XML (except in its XML serialisation) and has its own parsing rules.
Also, in which case is XML better than a database to transfer information inside a Web application?
XML is a good basis for a data exchange format. It is not a good basis for storing data in order to search it (which is what happens "inside" most web applications)
HTML and XML both come from SGML, hence their similarities. But XML is a strict grammar (no predefined tag names), while HTML is both a not very strict grammar and a vocabulary (tag names). There is an HTML variant which strictly complies with XML rules : XHTML.
As for using XML as a database, it is possible under certain circumstances. But it really depends on your architecture, language, volumetry and lots of other considerations. I suggest you open a new question with more details for this.
XHTML is a reformulation of HTML as XML app.
You can invent your own tags. I don't think HTML5 has a doctype for that though. You can create them with JavaScript and initalize/style then with CSS like any other element.
instead of using XML, spit out JSON, seriously, do this.
if you are worried about using your db, think about switching to couchdb or nosql. they're ripe for JSON.
don't get me wrong, your thought process isn't wrong, you can do that. i've seen it done rather well. but most people don't get it right. and seriously, JSON is your friend.
For the differences between HTML & XML see:
http://www.w3schools.com/xml/xml_whatis.asp
XML is primarily used for transfering data, not storing it. A database will generally give you much more flexibility in querying the data.
HTML allows things that XML doesn't allow, like omitting end tags, omitting the quotes around attribute values, and using upper-case and lower-case interchangeably. So HTML is not just another XML vocabulary.
XHTML, however, was an attempt to reformulate HTML as an XML vocabulary.
From time to time, I see web pages whose content is solely written in XML (not HTML or XHTML). These pages usually have some style sheets (either XSLT or CSS) attached to them which makes them look like any other ordinary web page.
My question is, what are the advantages of such an approach (if any), and why would anyone choose to work this way?
EDIT: If this is a good thing, why is it not widespread?
EDIT 2: Thanks everyone for the great responses. They really enlightened me. I also found this question whose content is also related.
It's easier to generate it programmatically and reuse it for other purposes than displaying as webpage.
Update:
EDIT: If this is a good thing, why is it not widespread?
Not everyone needs to generate it programmatically or reuse it for other purposes than displaying as webpage. It's then easier to use plain HTML.
One possible advantage would be for use of the data of the page in something other than a web browser; that would (presumably) be easier to do if a page's content were well-formed XML. Of course in theory a well-formed, semantic XHTML page should be nearly as able to be parsed, as well.
It can also be easier to generate XML instead of XHTML, depending on the data source.
When you are getting XML data in to your system, and you are supposed to present this XML data then it is much easier to write some XSLT for that XML instead of parsing it using some sort of parser and then presenting the data.
That can be a valid point for using XML instead of XHTML or HTML
Update
To answer your question on why this is not widespread, is because XSTL is tedious and hard to work with. Specifically XPath, which can be for some people quite difficult to use.
Those pages use XSLT to get rendered on the client side. Not every browser (especially older ones) supports rendering XML + XSLT. XML can however be used server-side as template and get transformed to HTML by the application running on the server. I personally don't see any advantages to this approach.
There are a lot more web pages that are written solely in XML than you know. You're only seeing the ones that do the XSLT transformation on the client side. Server-side transformation of XML is not at all unusual, because there's a plethora of things that produce data in XML, and transforming XML to HTML in XSLT is straightforward. You'll never know this is happening if you just look at the HTML, which bears no signs of having been generated via XSLT.
Personally, I don't understand it either though one of the biggest problems is support in IE. I created a skeleton ecommerce site serving XML, transformed by XSLT and styled using CSS. I sorely missed the ability to use XLink and other wonderful XML features. It's also nice to be able to tag the data for what it is. I used a 'menu' tag for the restaurant menus. 'price' tags for prices and so on. If a user clicked on a link to change menus, all I had to do was send the name of the item, the price and the description instead of the complete page. iirc, a 4K or more HTML menu page was only 200 bytes of sent data.
As far as the "one error makes everything crash in XML" type comments, the same is true of any programming language so proper coding should be no bother for programmers and careful HTML/CSS types.
Before anyone says that what I did was actually XHTML...no. I served XML. I did call up XHTML namespaces when needed for links, images and HTML type things but only when necessary.