com是microsoft以前极力推崇的东西，所以在windows操作系统中无处不在，同样delphi的vcl也有调用windows com服务的，最明显例子就是组件栏ado页的所有ado组件，如tadoquery，它是从tcustomadodataset继承下来的，而tcustomadodataset的定义如下：
tcustomadodataset = class(tdataset, iunknown,
recordseteventsvt)
private
frecordsetobject: _recordset;
ffindcursor: _recordset;
flookupcursor: _recordset;
flockcursor: _recordset;
frowset: irowset;
faccessor: iaccessor;
frowsetfind: irowsetfind;
fhaccessor: haccessor;
folerecbufsize: integer;
