Essential ADO.NET

1.4. Hierarchies, Objects, and Hybrids

Now let's explore ADO.NET's support for data models that predate the relational model. These ancient data models may bear some resemblance to more modern data models, and so it's instructional to see why they were used (and still are used, although to a lesser extent).

Early databases consisted of flat files with indexes, much like desktop databases such as Microsoft Access and Lotus dBase. IBM introduced the ISAM (Indexed Sequential Access Method) file access method to complement its Basic Direct Access Method (BDAM). BDAM files use pointers to physical cylinders and tracks on disk to index data. To move a file from one place to another, users must employ utilities that “fix” the physical pointers as they ...