Software & Development Tips

Extensible Mark-up Language (XML) has very quickly established itself as a viable technology with a huge range of real-world applications. One of the main reasons for its importance and wide acceptance is the fact that it offers a working solution to one of the key problems faced by software developers and computer users alike: the exchange of incompatible data. Each software environment creates its own unique type of binary file which only it can understand. When data is exported in XML format, it becomes a known quantity, independent of the environment in which it was originated.

Adobe’s PDF format is another example of a platform-independent data format which has gained wide acceptance. When a document is saved as a PDF file, its format is set in stone, it can viewed and printed with its layout and formatting intact, without the need for the software which created the original file. However, whereas the PDF format concerns itself primarily with the presenting information, XML is used to describe and encapsulate the information itself.

Though XML itself is still fairly new, the idea behind it is not. Back in the 1970s, Standard Generalized Markup Language (SGML) was developed in an attempt to create an application-independent method of describing data. SGML is a text-based language which uses the concept of adding mark-up to data which describes the data itself. An SGML document contains both data and a set of rules defining the structure of the data. SGML is a pretty complex language and, unlike XML, has never become mainstream. In the early 1990s, SGML was used to develop HTML and in the late 1990s, SGML was also used as the basis for the development of XML. So, basically, XML is a restricted form of SGML.

XML has already proved itself to be an excellent medium for storing, describing and transporting data, particularly over the web. It offers developers flexibility, clarity and simplicity. An XML document resembles an HTML document and consists of the same human-readable tags. However, the tags used to markup an HTML document are predetermined: only a fixed set of tags can legitimately be used. XML allows you to create your own markup language and define the tags which are legitimate for your data. It does this via the mechanism of a schema document, which can itself be an XML document. The schema document defines the vocabulary and grammar which may be used within the XML document containing your data.

The fact that, when creating and generating XML documents, you can invent all the rules, means that you never have to force your data into a container which was not designed to hold it. You design tags which reflect the nature of your data; you create a schema document which defines the hierarchical structure of your information; and you specify the type of information each element within your document is permitted to contain. In short, if you end up with an XML documents which is unsuitable for holding your information, you have only yourself to blame!

The writer of this article is part of an organisation that offers web design training courses in London and throughout the UK.

Displaying information on a web page which comes from a database is a fairly standard requirement on most websites and, in some development environments, it can take a fair amount of programming to achieve. In ASP.NET, however, it is remarkably easy, thanks to the use of built-in data-bound controls. There are two types of data-bound controls: those which are designed to display multiple records and those which will display one record only. The GridView control, the workhorse of databinding in ASP.NET, falls into the first category. It automatically generates an HTML table and fills it with information from a given data source with each record in the database rendered as a row in the table.

When using Visual Web Developer the easiest way to create a GridView control is simply to explore the appropriate data source using the database explorer, then drag the appropriate table or view onto the page. This action creates both a DataSource object and a GridView object, both of which can be customised either in Design or Source view. If the listing you wish to display on the page is to be tabular, you may not need to change the default GridView. However, it is more usual that you will want to customize the way in which data is displayed.

The first step in customization is often to turn off the automatic display of all the fields in the database as columns in the HTML table. This is done by setting the GridView’s AutoGenerateColumns attribute to False. Secondly, we can display data in a number of different ways. By default information is displayed in a BoundField, meaning that the data is displayed as text. By default, the heading displayed at the top of each column is simply the name of each field in the database. However, you can modify this by changing the HeaderText property of each BoundField element. Another useful property is DataFormatString which allow you to use a format string to control the display of data.

Where appropriate, you can also display data in a choice of other HTML formats: CheckboxField, RadioButtonField, HyperlinkField, ButtonField and ImageField. The final type of field is CommandField which enables you to display links enabling the user to edit, delete or select rows of data.

The GridView control also offers the TemplateField which allows you to place any HTML content you like in a given column and use databinding statements to embed information from the database as required. Template fields can even contain ASP.NET server controls.

The author is a trainer and developer with Macresource Computer Training, an independent computer training company offering ASP.NET training courses in London and throughout the UK.

categories: asp.net,web development,microsoft,computers,software