30-06-2012, 04:06 PM
DDBMS Architecture
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Definition
Architecture: The architecture of a system defines its structure:
– the components of the system are identified;
– the function of each component is specified;
– the interrelationships and interactions among the components are defined.
• Applies both for computer systems as well as for software systems, e.g,
– division into modules, description of modules, etc.
– architecture of a computer
• There is a close relationship between the architecture of a system, standardisation
efforts, and a reference model.
Motivation for Standardization of DDBMS Architecture
DDBMS might be implemented as homogeneous or heterogeneous DDBMS
• Homogeneous DDBMS
– All sites use same DBMS product
– It is much easier to design and manage
– The approach provides incremental growth and allows increased performance
• Heterogeneous DDBMS
– Sites may run different DBMS products, with possibly different underlying data models
– This occurs when sites have implemented their own databases first, and integration is
considered later
– Translations are required to allow for different hardware and/or different DBMS
products
– Typical solution is to use gateways
) A common standard to implement DDBMS is needed!
ANSI/SPARC Architecture of DBMS
• ANSI/SPARC architecture is based on data
• 3 views of data: external view, conceptual view, internal view
• Defines a total of 43 interfaces between these views
Architectural Models for DDBMSs . . .
• Autonomy: Refers to the distribution of control (not of data) and indicates the degree to
which individual DBMSs can operate independently.
– Tight integration: a single-image of the entire database is available to any user who
wants to share the information (which may reside in multiple DBs); realized such that
one data manager is in control of the processing of each user request.
– Semiautonomous systems: individual DBMSs can operate independently, but have
decided to participate in a federation to make some of their local data sharable.
– Total isolation: the individual systems are stand-alone DBMSs, which know neither of
the existence of other DBMSs nor how to comunicate with them; there is no global
control.
• Autonomy has different dimensions
– Design autonomy: each individual DBMS is free to use the data models and
transaction management techniques that it prefers.
– Communication autonomy: each individual DBMS is free to decide what information
to provide to the other DBMSs
– Execution autonomy: each individual DBMS can execture the transactions that are
submitted to it in any way that it wants to.