Directed Database object
The databases with objects are another particular case of the databases.
In such an organization, the data are represented in the form of objects.
An object (cf Directed object) represents a thing of the real life, concrete or abstracted like a person, a connection ftp or the sky.
The objects contain the data which describe them and which represent to them state . The object “sky” contains for example a variable which stores its color.
The objects contain also the logical which makes it possible to use them and to modify them. One can for example ask the sky to change color into sending a message mentioning to him the new color to be used.
All these entities are classified hierarchically in a database with objects. For example, the object “building” contains several objects of the type “stages” and each stage object contains several objects “office”. One then asks the offices to store the objects “nobody” to keep trace of the assignments of people. What gives:
building has \--> stage 0 --> stage 1 \--> office has \--> nobody Louse --> office B --> stage 2
Also think of the tree structure of the repertories and files in your computer. This kind of organization is done naturally in a database with objects whereas in other systems of bases, it is necessary to keep trace of which is the father and which is the wire.
But there needs sometimes also to find the data as in a relational base, for example. One could then have another object which will keep up to date the list of the people with the way to be traversed to find them, independently of their assignment or then with search criteria.
When the objects which one creates remain stored in the database with objects and not only in the Random access memory, one says that they are persistent .
Examples of directed databases objects
One of the best examples of DBMS directed object is the system O2.
It was carried out by the Grouping of Public interest ALTAIR, gathering IN2, the INRIA and the Research laboratory in Data processing of the University of Orsay. It was initially marketed by the company O2 Technology, then by the company Ardent Software and finally by the Informix company.
O2 has a language of description of diagram and of a computer programming language baptized O2C and which is an extension of the language C. an application written out of C or C++ can use the O2 services to ensure the persistence of its data. A query language of the type SQL called OQL could be used in an interactive way or inside a C++ program or O2C.
Since 1999 however, O2 is not marketed any more.
In a more concrete case, there exists a waiter of Web applications of the name of Zope, which uses a hierarchical database with objects coupled to an environment of development.
The most known examples at present basic of directed data objects are the directories, which are able to store a multitude of information. They store information in " objets" , very often an individual record sheet, a machine, a resource… with which one associates values, its attributes.
The directories are used everywhere at present; this more particularly in the world of the company, to store specific information to each person (name, first name, function, address, numbers, rights, accounts, etc)
There exists a multitude of protocol of directories, of which most known are LDAP, and its ancestor, X.500.
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