s BUILDING A SAMPLE APPLICATION WITH ASP.NET AND ATLAS in Java

Encoder Data Matrix in Java s BUILDING A SAMPLE APPLICATION WITH ASP.NET AND ATLAS

The application is built as a typical n-tier application comprising a resource tier that contains the back-end resources. In this case, the resources are the Company Information web service (courtesy of Flash-db.com) and the Price History web service that provides comma-separated values (CSV) over HTTP from Yahoo. You can see the architecture in Figure 11-2.

In a multitiered architecture like this, the resource tier is where the information that drives your service comes from. In many applications, and this one is no exception, the information is read-only you are simply presenting the resources to the end user. However, rarely are the raw resources presented. Some value has to be added to show how you visually present them and also how you enhance them for presentation using business logic. Many applications blur the distinction between business logic and presentation logic, but it is important to distinguish these, and indeed, when using Atlas, the ability to distinguish them becomes a lot easier. This is because before Ajax and Atlas, a developer would have to make a full-page refresh whenever the user interacted with the page. Then, with the advent of DHTML, they could make a decision for a simple interaction and for a simple business logic, it might be easier not to do it on the server but instead to do it using a script on the page. For example, if the current price for the stock is on the page, the current earnings are known to the page, and the user wants to display the profit/earnings (P/E) ratio (which divides the former by the latter), why not just calculate it using an on-page JavaScript and then render it in a <div> element instead of performing yet another round-trip to the server and producing a blink as the page refreshes This can quickly lead to a maintenance nightmare and is a common problem that has been solved by asynchronous updates. Now, even though in the previous scenario you may

incur another request to the server, the packet of information will be a lot smaller because you are just going to update part of the page; the entire page will not flash as it refreshes the user interface with the update. Beneath the resource tier comes the data retrieval tier. In a clean architecture, this is kept separate from the logic so that if data sources change, you do not need to get into the business logic plumbing and rip it out. It should provide a clean interface to the data layer. Visual Studio 2005 offers you the facility to create a proxy to an existing web service, which you can use to implement a data retrieval tier. In this application, the Price History web service from Yahoo provides CSV over HTTP so you will implement a web service that wraps this function, ality and can easily be proxied. The business logic tier is where you add value to your resources through aggregation, integration, and calculation. For example, in the case of calculating the P/E discussed earlier, with price information coming from one resource and earnings from another, instead of integrating and calculating these on the page level, you would aggregate the information in the business logic tier where the function performing the calculation would call the data retrieval tier to get the information from both resources and then perform the calculation. It would then provide the resultant information to the presentation tier as a response to the original request for the P/E analytic. The presentation tier is typically server-side logic that provides the markup and/or graphics that will get rendered in the browser. This can be anything from a C-based CGI service that generates raw HTML to an advanced control-based ASP .NET 2.0 server application. In this case, the example will use a variety of technologies, from ASP .NET controls that will render HTML that is generated by server-side C# code to advanced graphics functionality that renders the time series chart (you can see these charts in Figure 11-1). Finally, what appears to the user is the output of this presentation tier, and it is a document that contains HTML, graphics, JavaScript, style sheets, and anything else the browser needs to render. As I show how to construct the application, you ll see each of these tiers in a little more detail.