Posts Tagged 'XML'

February 2, 2011

API Basics: What is SOAP?

What is SOAP?
"Simple Object Access Protocol" - SOAP is a method and format for sending XML from one server to another via HTTP. SOAP allows you to have remote database servers which supply information to power your website. The best part about SOAP is that it is universal and secure. This means that big companies like SoftLayer can open their databases for you to gather the information that you need to keep your customers up to date. This kind of complete transparency is what makes SOAP (and any other supported API) an invaluable asset to SoftLayer customers. In order to fully understand SOAP, you will need to know about markup languages, namespaces and a little about the protocols used to implement it.

Markup Languages?
The term "markup language" is derived from when teachers/editors would make corrections to a written article, using shorthand for what needed to be corrected. A markup language is just a document with a few special symbols used to separate some text as "markup;" this text can then be used by other programs to perform tasks. Markup languages are declarative programming languages, so they contain data and talk about data, but they don't actually have instructions about what to do with the data. HTML, XML and LaTeX are all variations of markup languages.

Markup languages can be used for all kinds of different things, but the most common markup language used in web design is Hyper Text or HTML. HTML uses predetermined markup "tags" to describe data for browsers to display; it is the basic building block of all websites. SOAP uses XML to transfer data from server to server.

What is XML?
"Extensible markup language" - XML is a markup language dedicated to presenting data to different applications. Unlike HTML, XML has no dedicated markup tags; instead, you can create any type of tag you want. In XML, the tags describe and define the data that they contain. Applications can easily pull just the data that they need, no matter what is in the document. In this way an XML can be expanded without causing application errors, making it "extensible." Due to the free form of XML tags, sometimes you want multiple tags to have the same name; this is possible with XML namespaces.

How do XML Namespaces work?
Namespaces are used to group XML elements so that parsing programs won't confuse different elements that have the same name. Namespaces have to be defined by a "universal resource identifier" or URI; essentially, they have to be universally unique. This is why the WC3 chose to use website URLs as the standard naming convention. This can lead to some confusion when looking at XML namespaces, though. Information is not transferred to or from the websites; they don't even have to resolve, parsing programs read the URLs as basic text strings. SOAP uses a few pre-determined namespaces to define key information, but the most important thing about SOAP is its ability to work as an RPC-type protocol.

RPC?
"Remote procedure calls" are connections created between two or more servers for the sole purpose of enacting programs or procedures on a remote server. RPCs start at the client, sending a request to the remote server with a procedure name and perameters for the procedure. The request has to be in a very strict format, that way the host server doesn't have to know anything about the language that the client is using. SOAP makes RPCs over HTTP because it is the most accessible protocol; very few firewalls block HTTP, and SOAP makes use of headers similar to HTTP headers to provide encoding and security information.

So, What is SOAP?
In short, SOAP is a very strictly formatted XML document which uses XML namespaces to define key elements of data, sent via HTTP, in order to enact procedures on a remote server, and sometimes receive data in response to those procedures.

-Kevin

January 19, 2011

AJAX Without XML HTTP Requests

What is AJAX?

Asynchronous JavaScript and XML - AJAX - is what you use to create truly dynamic websites. Ajax is the bridge between application and presentation layers, facilitating lightning fast, instant application of data from the end user to the host and back to the end user. It dynamically changes the data displayed on the page without disrupting the end user or bogging down the client. Although the name is misleading, it is used as a term for any process that can change the content of a web page without unnecessarily reloading other parts of the page.

What are XML HTTP requests?

Passing information from your server to your end user's browser is handled over HTTP in the form of HTML. The browser then takes that info and formats it in a way the end user can view it easily. What if we want to change some of the data in the HTML without loading a whole new HTML document? That's where XML comes in. Your web page needs to tell the browser to ask for the XML from the server; luckily, all browsers have a function called XmlHttpRequest(). Once it's called, it will poll the server for XML data.

Why shouldn't you use XML HTTP requests?

A long time ago, in a galaxy far, far away, Microsoft invented the XmlHttpRequest() object for Microsoft Exchange Server 2000. As with all first generation technologies, everyone wanted to use it, and some people implemented it differently. IE didn't even have native support until 2006, and there are still some discrepancies in various browsers when studying the OnReadyStateChange event listener. There is also an issue with cross-domain requests. When the internet was young, JavaScript hackers would steal users' identity by pulling information from secure websites and posting it to their own, stealing bank account numbers, credit cards, etc. Now that the internet has grown up a bit, people with large networks and many servers have found use for sending data across domains, but it's still not possible with XML HTTP requests.

What's an Alternative?

Using JavaScript, you can create client side scripts whose source is built with server side scripts, passing variables in the URL. Here's an example of a basic web page with local JavaScript, a few checkboxes for human interaction, and a table with some information that we want to change. View source on the page below to see the outline.


Looking at the three JavaScript functions, the first (clearTags) automatically clears out the checkboxes on load, the second (check(box)) makes sure that only one box is checked at a time, the third (createScript) is the interesting one; it uses the createElement() function to create an external JavaScript, the source of which is written in PHP. I have provided a sample script below to explain what I mean. First, we get the variable from the URL using the $_GET super global. Then, we process the variable with a switch, but you might use this opportunity to grab info from a database or other program. Finally, we print code which the browser will translate to JavaScript and execute.

<code>&lt;?PHP
//First we get the variable from the URL
$foo=$_GET['foo'];
//Here's the switch to process the variable
switch ($foo){
case 'foo' : print "var E=document.getElementById('data'); E.innerHTML='bar'; "; break;
case 'fooo' : print "var E=document.getElementById('data'); E.innerHTML='barr'; "; break;
case 'ffoo' : print "var E=document.getElementById('data'); E.innerHTML='baar'; "; break;
case 'ffooo' : print "var E=document.getElementById('data'); E.innerHTML='baarr'; "; break;
default : print "var E=document.getElementById('data');
E.innerHTML='unknown'; ";
}
?&gt;
</code>

-Kevin

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