As a result each level gets increasingly complex. An example is the file structure on a typical computer. Hierachical files can be inefficient in some respects. It is difficult to allow for redundent data. Searching in a hierachial file can also be inefficient since searching may require looking down mutiple levels repeatedly.
Relational databases are an extension of the flat file.
It consists of a series of related tables. The tables are interconnected via a key field. Use of the key field allows the combination of the tables by indexing against the key field. The relational database was introduced in 1970 and is currently the most popular method used. Questions for Database Concepts Describe the differences between vector and raster data structures.