Building a 21st Century Application
In previous issues of Component Developer Magazine, we have introduced technologies such as Queued Components, COM+ Security, Loosely Coupled Events, SQL Server 2000 and BizTalk Server. Each of these represents a fascinating myriad of possibilities. But, how do you put all of them together to build a real-life, highly reliable, 100% available distributed application?
In this article, I will take you through the steps of building a small application from start to finish. Since I don't want to turn this into a novel, I chose a relatively simple scenario that allows employees to order supplies from various vendors. Our little application will store all items and orders in a SQL Server database, which we will access using SQL Server 2000's XML features. A core business object will handle all communication with the database. This business object is a COM+ Component, running in a secure environment with COM+ Security. To ensure flexibility, our business object will fire loosely coupled events that could be used in the future to extend the system.
When a user attempts to place an order, COM+ Security will determine whether or not the user is allowed to place an order, and if so, will make sure the order amount is within the user's limits. If the user is allowed to place the order, we will utilize Microsoft BizTalk Server 2000 to communicate with the appropriate vendor, placing the order in a fully automated fashion.
I will illustrate several different ways of interacting (interfacing) with this system. First of all, we will provide a rich client implemented as a regular Windows form. Each user who wants to use this interface will have to run a small setup program to install the client application on his computer.
This extra step adds a very important ability: It allows us to use Queued Components to communicate with the server, even if the client application is on a notebook computer that is temporarily disconnected from the server.
While the rich client solution is great for those who use our system a lot, it is somewhat inconvenient for employees who use the system on an irregular basis. We do not want to make these people go through the setup routine. Instead, we will provide a web interface they can use by simply navigating with their web browser. Although this requires connectivity to use the system, it's a great solution for employees who don't travel and don't have the need to place orders while disconnected.
I'm sure you can envision a number of other possible interfaces for this application, such as wireless devices and a voice interface. I do not intend to provide those interfaces here, but I will design the system to be open for people who want to write those interfaces. For this reason, we could make the business object available as a Web Service. However, due to space limitations, I won't be able to cover that in this article. (If you are interested in Web Services, see Rick Strahl's article in the Issue 1 - 2001 issue.)
Figure 1 provides an overview of the system architecture.
Figure 1: All the logic of our application lives in a COM+ business object. This object communicates with SQL Server 2000 as well as BizTalk Server to store and place the orders. For maximum flexibility, we implement COM+ Events and make the object available as a web service. We also provide two standard interfaces: A Windows form and a web page.
By: Markus Egger
Markus is the founder and publisher of CODE Magazine and EPS' President and Chief Software Architect. He is also a Microsoft RD (Regional Director) and the one of the longest (if not THE longest) running Microsoft MVPs (Most Valuable Professionals). Markus is also a renowned speaker and author.
Markus' spends most of his time writing production code. The projects Markus has worked on include efforts for some of the world's largest companies including many Fortune 500 companies. Markus has also worked as a contractor for Microsoft (including the Visual Studio team). Markus has presented at many industry events, ranging from local user groups to major events such as MS TechEd. Markus' written work has been published extensively and in magazine ranging from MSDN Magazine, to Visual Studio Magazine, and of course in Markus' own CODE Magazine and much more. Markus is a supporter of communities in North America, Europe, and sometimes even beyond.
Markus currently focuses on development in .NET (Windows, Web, Windows Phone, and WinRT) as well as Android and iOS. He is passionate about overall application architecture, SOA, user interfaces and general development productivity and building maintainable and reusable systems.
In his spare time, Markus is an avid windsurfer, scuba diver, ice hockey player and world traveler. On a rainy day, he is known to enjoy a good game on his PC or Xbox.
SQL Server 2000, Queued Components, COM+ Security, BizTalk Server, and similar technologies make it easy to build a highly reliable and highly available distributed application.