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Connecting to a database. BDE? ADO?
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Page 1: Delphi database connectivity.
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As shown in the previous chapter of this course, a database is a collection of one or more tables that store data in a structured format. These tables, contain data that is represented by rows and fields. When a database consists of two or more tables, these tables generally contain separate yet related data. MS Access, Interbase or SQL Server use a single file (Access, the *.mdb file) that represents the entire database. On the other hand, Paradox and dBase databases are defined with separate tables and files that represent indexes and table relations. All the files needed to describe a Paradox database are usually stored in a single directory. Delphi, of course, has means of working with both approaches.
With Delphi, we can connect to different types of databases: local or client/server (remote server) database. Local databases are stored on your local drive or on a local area network. Remote database servers usually reside on a remote machine. Types of local databases are Paradox, dBase and MS Access. Types of client/server databases are MS SQL Server, Interbase or Oracle.
Local databases are often called single-tiered databases. A single-tiered database is a database in which any changes, such as editing the data, inserting records, or deleting records - happen immediately. Single-tiered databases are limited in how much data the tables can hold and the number of users your application can support. When the database information includes complicated relationships between several tables, or when the number of clients grows, you may want to use a two-tiered or multi-tiered application. Client applications run on local machines; the application server is typically on a server, and the database itself might be on another server. The idea behind the multi-tier architecture is that client applications can be very small because the application servers do most of the work. This enables you to write what are called thin-client applications.
When we write a database application in Delphi, we need to use some database engine to access a data in a database. The database engine permits you to concentrate on what data you want to access, instead of how to access it. From the first version, Delphi provides database developers with the BDE (Borland Database Engine). Beside the BDE, Delphi from the fifth version supports Microsoft ADO database interface.
This course will primarily focus on MS Access local database producing the single-tiered application.
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