Hierarchical database
A hierarchical database is a Database whose management system binds the recordings in a Tree structure where each recording has one possesseur. For example, the duck belongs to the family of the anatidés which itself belongs to the order of the ansériformes which itself belongs to the class of the birds which itself belongs to the subphylum of the vertebrate which itself belongs to the animal reign .
The structures of data hierarchical were largely used in the first basic management systems of data of the type Mainframe . They however showed limits to describe complex structures, to meet the real needs and to follow the evolution of the information systems. As one sees it in example referred to above, organization hierarchical of databases is particularly adapted to modeling of Nomenclature S , but if the principle of relation “1 towards NR” is not respected (the duck does not belong although with only one family but, for example, a sick can be in relation to several doctors ), then the hierarchy must be transformed into a network.
This evolution necessary will give rise to the relational databases.
Terms employed
- Field (Field) - the smallest unit of data
- Segment - group of fields; node of a tree structure
- Went back base record - a collection to dependant segments; a particular tree structure
- Went back base (database) - together to “dated base records”
- Data base description - the way indicates in which them “base records dated” are defined; together of instructions of the language of macro owner
- Root (root) - the first “segment”
- Sequence field - a field of each “segment” used to organize the other fields in the same way standard
Some widespread examples of hierarchical databases
- , Adabas
- IMS or DL/1 (of IBM)
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