Crucially, it encompasses a number of tools and services that are enabling technologies - they make it possible to concentrate on the business requirements and code of a distributed application, and not have to worry too much about the plumbing of what goes where and how it works.

So, for example, some of the services make it simple to make certain parts of our project take part in transactions, and those services will control any transactions that take place. We just have to concern ourselves with deciding which parts of our project should take part in transactions, not how to control transactions in software.

The Windows DNA concept is now evolving into Windows DNA 2000 which is both a marketing term devised by Microsoft to help promote the Windows 2000 family of operating systems and a reference to the development of the original tools and services into a complete development platform.

The Microsoft Solutions Framework (MSF) Application Model we referred to above consists of a logical 3-tier services-based approach to designing and developing software applications, using Windows DNA.

The overall architecture looks very familiar. However, as we'll discover, the tools and services that underpin the whole architecture make developing complex applications quite straightforward:

Let's overview the tools and technologies associated with this approach. We won't be making use of all these technologies (some of them are for more advanced development than we're doing here), but we'll quickly introduce most of the names.

Windows DNA

Windows DNA, or, as it's becoming, the Windows DNA 2000 platform, is supported by a comprehensive set of application services on the Windows operating systems. As we said, the basic idea behind Windows DNA is to provide us, as developers, with a set of tools enabling us to easily create the application infrastructure, so that we can concentrate on the logic that's specific to the business problem being solved. These infrastructure services are covered in more detail in later chapters as we use them, but they include support for building Web-based applications, support for transactions, and a unifying component model.

With the release of Windows 2000 and associated products this area is in a state of transition, and the precise technologies you're likely to use to develop an application will depend on the platform your client is using. Of course there is an easy migration path between the different technologies, and in this book we'll show you how to develop for both Windows 9x/NT 4.0 and Windows 2000 platforms.

So, for 3-tier development in a Windows 9x/NT 4.0 environment the tools at our disposal include:

• Microsoft Transaction Server (MTS) - A rich set of integrated services that makes it easy to build multi-user server-side components and perform transactions across multiple data sources
• Microsoft Internet Information Server (IIS) - Web server software
• Active Server Pages (ASP) - A server-side scripting technology that makes it easy to build Web pages that are both dynamic and interactive
• Microsoft Component Object Model (COM) - A foundation for creating distributed applications built from components
• Microsoft Message Queue Server (MSMQ) - A flexible, reliable approach to communication between applications
• Universal Data Access (UDA) - A set of data access services, including an easy-to-use high-level programming interface ActiveX Data Objects (ADO)
• Microsoft SQL Server 7.0 - A relational database management system for the Microsoft Windows platform

In Windows 2000 there are the following variations:

• MTS has been merged with COM and is part of COM+
• IIS is called Internet Information Services

With the exception of SQL Server 7.0, all these technologies are currently included with the Windows 2000 Server series of operating systems. However, the situation is slightly different for users of Win 9x or NT 4.0. We'll discuss exactly what software you need to make the most of this book (and how to obtain it) at the end of the chapter.

Let's now expand slightly on what these technologies can do for us, and where we are likely to encounter them.

Microsoft Transaction Server (MTS)

Microsoft Transaction Server (MTS) delivers the plumbing for multi-user server applications, including transactions, scalability services, connection management, security contexts, and point-and-click administration. This provides us with an easy way to build and deploy scalable server applications, and to build single-user components that can be made multi-user merely by hosting them in MTS. MTS also provides a security context for the components that it manages, which enables the components to run in a required security context regardless of the security context of the client.

We'll be looking at MTS in detail in Chapter 5, and we'll use it within our case study to support the activities that form our Business and Data tiers.

In Windows 2000, MTS has been consolidated with COM into COM+, a unified programming model that we discuss in a moment.

Internet Information Server (IIS)

Microsoft's Internet Information Server/Services (IIS) enables the development of Web-based business applications that can be extended over the Internet or deployed over corporate intranets. Internet Information Server integrates with MTS and ASP, and this integration has introduced a new concept to the Internet-transactional applications.

We'll be using IIS (or one of it's close relations PWS) in Chapter 17 when we Web-enable our case study.

Active Server Pages (ASP)

Active Server Pages (ASP) is the critical technology for server-side scripting in Microsoft's web strategy. This technology is used to create and run dynamic, interactive Web server applications, and we'll make extensive use of ASP when we Web-enable the case study in Chapter 17.

ASP page scripts can be written using VBScript (the default), JavaScript, or other scripting languages. ASP pages are especially useful in creating dynamic interactive Web content that will run on any browser, as all the processing occurs on the server before the resulting Web page is served up to the browser.

Component Object Model (COM)

The Component Object Model (COM) is Microsoft's standard set of specifications that allows components to communicate with each other. It is language independent, so components created using Visual Basic can work with components coded in, say, C++. Of course, here we'll be building our components in VB, and we'll spend a lot of time in Chapters 12 and 13 coding components to act as our Data tier and our Business tier.

Microsoft Message Queue Server (MSMQ)

Message queuing is another feature of the Microsoft Windows Server operating systems. Microsoft Message Queue Server (MSMQ) helps to integrate applications by implementing a business event delivery environment where messages can be sent between applications. It also makes it easier to build reliable applications that will work over networks that may not be as reliable as we would wish.

This simple application, based on the Component Object Model, lets developers focus on business logic, not sophisticated communications programming. MSMQ, while being extremely useful, lies outside the scope of this book.

Universal Data Access (UDA)

Universal Data Access (UDA) provides high-performance access to a variety of information sources, including relational (from sources such as SQL Server, Access or Oracle) and non-relational data (such as data from Active Directory, Microsoft Exchange, etc.). UDA also provides an easy-to-use programming interface, ActiveX Data Objects (ADO) that works with all programming tools and languages that support COM.

We're going to be encountering UDA and using ADO in Chapter 11.

SQL Server

SQL Server is a relational database management system for the Microsoft Windows platform. SQL Server delivers a flexible, powerful platform that scales up to terabyte-size (a terabyte is 1,000 GB) databases and down to small business servers and laptop databases. This product is going to provide the data store for our case study, and we'll be working with it extensively in Chapters 9 and 10.

COM+

COM+ is an extension to the Component Object Model (COM), and is shipping as an integrated component in Windows 2000 operating systems. This technology enables us to create distributed components that can interact over any network using the language of our choice.

The COM+ services delivered in Windows 2000 are the next evolutionary step of COM and MTS. The consolidation of these two programming models makes it easier to develop distributed applications by unifying the development, deployment, debugging and maintenance of an application that used to rely on COM for certain services and MTS for others.

COM+ is mentioned in Chapter 4 and covered in more detail in Chapter 5.

Well, we've mentioned it enough times, so let's see what our case study actually consists of.