HTML is predefined markup language. Small errors are ignored. Whitespace You can use whitespaces in your code. You can't use white spaces in your code. Nesting Should be done appropriately.
Does not have any effect on the code. The closing tag is not always required. Mostly using attributes and elements. Offers native object support Null support Need to use xsi:nil on elements in an XML instance document and also need to import the corresponding namespace.
Natively recognizes the null value. Namespaces XML provides support for namespaces. It helps you to remove the risk of name collisions when combining with other documents. Does not support the concept of namespaces. Naming collisions can be avoided either using a prefix in an object member name or by nesting objects. Formatting decisions Require more significant effort to map application types to XML elements and attributes.
HTML is a simple technology stack that is familiar to developers. With the help of XML, you can exchange data quickly between different platforms. HTML is easy to understand because it has a very simple syntax You can use many tags to make a webpage. Allows you to use various colors, objects, and layouts Disadvantages of using XML Here, are few drawbacks of using XML: XML requires a processing application The XML syntax is very similar to other alternative 'text-based' data transmission formats which is sometimes confusing No intrinsic data type support The XML syntax is redundant Does not allow the user to create his tags.
XML tags are not predefined. HTML provides support for multimedia embedding in documents With the help of XML, you can exchange data quickly between different platforms. What is Jenkins? Jenkins is an open source Continuous Integration server capable of orchestrating a In programming languages, functions can be invoked in two ways: which is known as Call by Value In this tutorial, you will learn select Filter Pipeline arrange The library called dplyr The markup may be a little cryptic, but if it's laid out properly it's pretty easy to follow.
That's an important point: The display is browser-independent. If there were a photo of the results of making this recipe and one certainly hopes there isn't , it would show up in a graphical browser but not in a text browser. There's one major problem with HTML as a data format, however. The meaning of the various pieces of data in the document is lost.
Now, the idea of data in an HTML document meaning something may be a bit hard to grasp. Web pages are fine for the human reader, but if a program is going to process a document, it requires unambiguous definitions of what the tags mean.
That's what the tag means, and it doesn't mean anything else. Sure, you could write a program that grabs the headers out of the document, reads the table column headers, figures out the quantities and units of each ingredient, and so on.
The problem is, everyone formats recipes differently. What if you're trying to get this information from, say, the Julia Childs Web site, and she keeps messing around with the formatting? If Julia changes the order of the columns or stops using tables, she'll break your program! Though it has to be said: If Julia starts publishing recipes like this, she may want to think about changing careers. Now, imagine that this recipe page came from data in a database and you'd like to be able to ship this data around. Maybe you'd like to add it to your huge recipe database at home, where you can search and use it however you like.
Unfortunately, your input is HTML, so you'll need a program that can read this HTML, figure out what all the "Ingredients," "Instructions," "Units," and so forth are, and then import them to your database. That's a lot of work. Especially since all of that semantic information -- again, the meaning of the data -- existed in that original database but were obscured in the process of being transformed into HTML. Now, imagine you could invent your own custom language for describing recipes. Instead of describing how the recipe was to be displayed, you'd describe the information structure in the recipe: how each piece of information would relate to the other pieces.
Let's just make up a markup language for describing recipes, and rewrite our recipe in that language, as in Listing 3.
It will come as little surprise to you, being the astute reader you are, that this recipe in its new format is actually an XML document. Maybe the fact that the file started with the odd header.
The semantics, or meaning of the information, is maintained in XML because that's what the tag set was designed to do. It's important to get some nomenclature straight. In Figure 1, you see a start tag, which begins an enclosed area of text, known as an Item , according to the tag name. The Item defined by the tag ends with the end tag. Not every tag encloses text. In XML, such elements aren't allowed. Instead, XML has empty tags, denoted by a slash before the final right-angle bracket in the tag. Figure 2 shows an empty tag from our XML recipe.
Note that empty tags may have attributes. Every XML document must be well-formed. What does that mean? Read on! The concept of well-formedness comes from mathematics: It's possible to write mathematical expressions that don't mean anything. For example, the expression. In other words, the "expression" above isn't well-formed. Mathematical expressions must be well-formed before you can do anything useful with them, because expressions that aren't well-formed are meaningless.
The most important of these rules are as follows:. You can get away with all kinds of wacko stuff in HTML.
XML doesn't allow this kind of sloppiness. Every start tag must have a corresponding end tag. This is because part of the information in an XML file has to do with how different elements of information relate to one another, and if the structure is ambiguous, so is the information. So, XML simply doesn't allow ambiguous structure. This nonambiguous structure also allows XML documents to be processed as data structures trees , as I'll explain shortly in the discussion of the Document Object Model.
A tag that opens inside another tag must close before the containing tag closes. For example, the sequence. The correct sequence must be. To represent these three characters left-angle bracket, right-angle bracket, and double quotes in the text part of the XML not in the markup , you must use the special character entities. These characters are special characters for XML.
An XML file using, say, the double quote character in the text enclosed in tags in an XML file isn't well-formed, and correctly designed XML parsers will produce an error for such input. Many vendors now offer XML parsers in Java for free; you'll find links to these packages in Resources at the bottom of this article.
XML parsers recognize well-formed documents and produce error messages much like a compiler would when they receive input that isn't well-formed. As we'll see, this functionality is very handy for the programmer: You simply call the parser you've selected and it takes care of the error detection and so on. While all XML parsers check the well-formedness of documents meaning, as we've seen, that all the tags make sense, are nested properly, and so on , validating XML parsers go one step further.
Validating parsers also confirm whether the document is valid ; that is, that the structure and number of tags make sense. Only one title or no title makes sense.
This XML document is certainly well-formed, but it doesn't make sense. It isn't structurally valid. The problem is, we have a document that's well-formed, but it isn't very useful because the XML doesn't make sense. We need a way to specify what makes an XML document valid.