Chapter 16: Multitier DataSnap Applications

Chapter 16: Multitier DataSnap Applications


Large companies often have needs that are broader than applications using local database and SQL servers can meet. In the past few years, Borland Software Corporation has been addressing the needs of large corporations, and it even temporarily changed its own name to Inprise to underline this enterprise focus. The name was eventually changed back to Borland, but the focus on enterprise development remains.

Delphi targets many different technologies: three-tier architectures based on Windows NT and DCOM, TCP/IP and socket applications, and—most of all—SOAP- and XML-based web services. This chapter focuses on database-oriented multitier architectures; XML-oriented solutions will be discussed in Chapters 22 and 23, which are devoted to XML, SOAP, and web services.

Before proceeding, I should emphasize two important elements. First, the tools to support this kind of development are available only in the Enterprise version of Delphi; and second, with Delphi 7 you don't have to pay a deployment fee for DataSnap applications. You buy the development environment and then deploy your programs on as many servers as you want, without owing Borland any money. This is a very significant change (the most significant in Delphi 7) to the distribution policy of DataSnap, which used to require a per-server fee (initially very high, then significantly lowered over time). This new deployment license will certainly increase the appeal of DataSnap to developers, which is a good reason to cover it in some detail.

Part I: Foundations