The LA Fox Developer Newsletter

February 2000

ADO Quickstart (Con’t from page 1)

VFPCOM.DLL achieves the same results. The topics VFPCOM,

ADO Events, and how to integrate ADO and Visual FoxPro will

be discussed in another white paper. This paper is dedicated to

providing the Visual

FoxPro developer, with a comprehensive overview of ActiveX

Data Objects, Remote Data Services (RDS), their respective

objects, and how those objects work.

What Are OLE DB and ADO?

When discussing ADO, we are really talking about two distinct

elements: the ActiveX data objects themselves and Microsoft

Universal Data Access technology, more commonly known as

OLE DB.

OLE DB and Universal Data Access

In simple terms, OLE DB is the succeeding technology to the

Open Database Connectivity (ODBC) standard. OLE DB is a set

of low-level interfaces that facilitate the Microsoft Universal Data

Access strategy. ADO is a set of high-level interfaces for

working with data.

While both ODBC and OLE DB have the ability to make data

available to a client, the capabilities of the two technologies are

very different. ODBC is primarily designed for use on relational

data. However, data exists in nonrelational as well as relational

formats. In addition to new data formats, data resides in new

places such as the Internet. Finally, the Microsoft Component

Object Model (COM) framework requires better data access

technology. Clearly, ODBC does not address these needs; a

new technology is needed. That technology is OLE DB, and it is

here to stay.

The following graphic best illustrates how OLE DB and ADO

work together. Clients can work directly with OLE DB or can

work with OLE DB through the ADO interface (the latter is

typically the case). Note that OLE DB can access SQL data

either directly or through ODBC. An OLE DB provider provides

direct access by OLE DB. Also note that OLE DB can also be

used to access a variety of non-SQL data, as well as data that

exists in mainframes. The ability to access data through a

common interface, without regard to data location or structure,

is the real power behind ADO and OLE DB.

(Con’t next column)

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Whereas ODBC uses drivers, OLE DB uses providers. A

provider is a software engine that provides a specific type of

data that matches the OLE DB specification. Several OLE DB

providers exist today, including those for Microsoft SQL

ServerTM and Oracle. Because there is such widespread use of

ODBC, an OLE DB provider for ODBC has also been created in

order to ease the migration from ODBC to OLE DB. Several

nonrelational providers are currently under development. Per-

haps the most anticipated of these is the OLE DB Provider for

Microsoft Outlook®. A special provider, MS Remote, allows

direct data access over the Internet. This brief list of providers

shows the third-party community commitment to OLE DB, and

many new providers are currently under development. For the

latest news on available providers, refer to http://

www.microsoft.com/data/.

ADO Overview

OLE DB is then a set of low-level interfaces that provide access

to data in a variety of formats and locations. While powerful,

OLE DB interfaces can be cumbersome to work with directly.

Fortunately, ADO provides a set of high-level, developer-friendly

interfaces that make working with OLE DB and universal data

access a relatively simple task. Regardless of the programming

environment you use, any Visual Studio® or Microsoft Office

product such as Visual FoxPro, Visual Basic, Visual C++®, or

Word, the interface you will use to access data remains con-

stant. That interface is ADO, which in turn uses OLE DB.

ADO itself is just a set of objects. By itself, ADO is not capable

of anything. In order to provide any functionality, ADO needs the

services of an OLE DB provider. The provider in turn uses the

low-level OLE DB interface to access and work with data. One

ADO connection may use a SQL Server OLE 06 provider and

another ADO connection may use an Oracle OLE DB provider.

While the interface is constant, the capabilities may be very

different because OLE DB providers are very different, which

highlights the polymorphic nature of OLE DB.

As developers, we crave consistency. ADO provides us with a

consistent interface for our program code.

ADO Version Summary

The current version of ADO (2.1) is the fourth version of ADO to

(Con’t, page 6)

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