What is it?
ADO (ActiveX Data Objects) is used by Web page developers to add database access to their online content. It is meant for "application and Web site developers with modest programming skills". You get ADO when you install Active Server Pages, Visual Interdev or the OLE/DB software developers kit.
Where did it originate?
The first of ADO's predecessors was DAO (Data Access Objects) , which came packaged with Access and Visual C++. But DAO was tied to Access, where ADO is intended to be database-independent.
DAO was a poor fit with Microsoft's ODBC (open database connectivity) API, which provides a common interface for databases from different suppliers. ODBC is also a pig to use, so, to kill two birds with one stone, Microsoft came up with RDO (Remote Data Objects), which arrived with Visual Basic Enterprise Edition.
Then OLE/DB appeared to be an obvious, object-based successor to the three technologies - but was even harder to work with than ODBC.
ADO is essentially an amalgam of DAO and RDO, providing a Noddy's interface to OLE/DB. It is intended to be easy for people familiar with DAO and RDO to work with. Ultimately, ADO will succeed all the others as Microsoft's data access standard. It uses the OLE Automation interface.
What's it for?
ActiveX Data Objects are ActiveX controls with no visual interface. Microsoft describes them as "programmable objects". They connect to databases, issue queries, and gather responses.
They offer the same interface and features, whether data is stored locally in Access or Foxpro, or in SQL Server, Oracle, Informix, or Sybase servers. ADO is also consistent across multiple programming environments, including VB, C++, Java and scripting languages and Microsoft's Active Server Pages.
What makes it special?
It is "Microsoft's data access model of the future", which will be able to access non-relational database sources, including e-mail.
As well as being simpler to work with, ADO uses a flatter object model than its predecessors, and so requires fewer lines of code and occupies less memory, which can be important for performance on a busy Web page.
How hard is it to master?
The standard textbook on the subject is called Teach Yourself Active Web Database Programming in 21 Days, however, people with more modest expectations should be able to get going more quickly.
Where is it used?
Where Web applications need to call database content. ADO is not restricted to Microsoft databases.
Not to be compared with
"Comparisons are odorous," said Dogberry, in Much Ado About Nothing.
What does it run on?
"Any" platform that supports Com and OLE. Other systems can access online content through ADO via a Web browser.
Few people know that
ADO, OLE, RDO is an anagram of O, EL DORADO, the mythical land we will get to when Microsoft finally sorts its object strategy out, where we will all be as rich as Bill Gates, but still work 20 hours a day and live on diet Coke and Snickers bars.
What's coming up?
Microsoft's.net initiative is based on Soap (Simple Object Access Protocol), a technology-neutral way to get objects running on different machines to interact with each other. Soap uses HTTP and XML. Microsoft has a fair amount of control over Soap, but has shown willingness to collaborate with IBM and others, and to change the protocol substantially to make it more open.
Rates of pay
You will probably have ADO as part of a package that includes a Microsoft language and/or database, and some knowledge of Com and ActiveX. The range for these skills is generally between £20,000 and £40,000, and, more precisely, £28,000 to £35,000 for those with a few years' experience.
Ask Microsoft's Developer Network training wizard about ADO, and it offers no results. What you need to know is spread in bits and pieces across a number of courses covering Com, languages such as Visual C++, and the Access and SQL Server databases. You will need to do bit of digging.
You can find out about Microsoft's Certified Technical Education Centres, and online and CD-based training offerings, at www. microsoft.com/train_cert/.
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