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in turn use techniques such as the generation of subsystems or the configura-
tion of subsystems out of reusable, already existing components [43].
12.4.5 Categories of Component DBMS Models
We now summarize and examine component DBMS models. Table 12.1
summarizes the characteristics of the four categories.
The categories listed in Table 12.1 are not necessarily disjoint. For
instance, it is conceivable that both plug-in components for nonstandard
data as well as wrappers for accessing external data stores can be added to a
single system. Such a system would therefore belong to the first two catego-
ries (e.g., as outlined in [47]). Likewise, OLE DB could also be classified as a
configurable DBMS, because in principle it allows the exchange and addition
of internal components, for example, to add specialized query processors.
12.5
Development of Component DBMSs and Their Applications
Given all the powerful new kinds of functionalities CDBMSs offer, the ques-
tion is apparent of how users can effectively use themwe encounter the
problem of design and development of component DBMSs and their appli-
cations. Because the type of systems considered here are only in the process of
Table 12.1
Classification of Component DBMS Models
Architecture,
Plugs
Category
Purpose
Typical Components
Plug-in DBMSs
Extend existing DBMS
with nonstandard
functionality
Interfaces expected or
provided by kernel
ADT definition and
implementation, new
indexes
Middleware
DBMSs
Integrate existing data
stores into DB system
Common format and
interfaces between
DBMS and wrappers
Wrappers for external
data sources
Service-oriented
architectures
Provide DB functionality
in standardized,
unbundled form
Service definitions
Service implementations
Configurable
DBMSs
Compose nonstandard
DBMS out of reusable
components
Service definitions
DBMS subsystems
