One of the original scopes of computer applications was storing large amounts of data on mass storage devices and retrieving them at a later point in time. Over time user requirements increased to include not only sequential access but also random access to data records, concurrent access by parallel (writing) processes, recovery after hardware and software failures, high performance, scalability, etc. In the 1970s and 1980s, the science and computer industries developed techniques to fulfill those requests.
Basic bricks for efficient data storage - and for this reason for all Database Management Systems (DBMS) - are implementations of fast read and write access algorithms to data located in central memory and mass storage devices like routines for B-trees, Index Sequential Access Method (ISAM), other indexing techniques as well as buffering of dirty and non-dirty blocks. These algorithms are not unique to DBMS. They also apply to file systems, some programming languages, operating systems, application server and much more.
In addition to the appropriation of these routines, a DBMS guarantees compliance with the ACID paradigm. This compliance means, that in a multi-user environment all changes to data within one transaction are:
A distinction between the following generations of DBMS design and implementation can be made:
... WHERE employee.department_id = department.id .... The consequence is that - with the exception of explicit foreign keys - there is no meaning of a parent/child or owner/member denotation. Relationships in this model do not have any direction.
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