Information Technology Reference
In-Depth Information
(i) Private data, i.e., personal daily schedules, phone numbers, etc.
(ii) Public data, i.e., news, weather information, traffic information, flight infor-
mation, etc.
(iii) Shared data, i.e., traditional databases, distributed, replicated, and/or frag-
mented across different geographic locations—a collection of processing
nodes may contribute, cooperate, and complete with each other to maintain
consistency and participate in distributed decision making operations.
The desire to support timely and reliable access to the information sources is not
an entirely new concept. Traditional databases based on fixed clients and servers con-
nected over a reliable network infrastructure have addressed the issues involved in
accessing various types of information in the form of relational, object-oriented, dis-
tributed, federated, and multidatabase management systems. However, the concept
of mobility, where a user accesses information through a remote connection with a
portable device, has posed several challenges on traditional database management
systems (DBMS). Within the scope of this infrastructure, two types of services are
available to the user:
On demand-based services; and
Broadcast-based requests.
1 . 1 O n D e m a n d - B a s e d S e r v i c e s
Private data and shared data are the subject of these services in which users obtain
answers to requests through a two-way communication with the database server—
the user request is pushed to the system, data sources are accessed, query operations
are performed, partial results are collected and integrated, and generated information
is communicated back to the user. This requires a suitable solution that addresses
issues such as:
Security and access control—methods to guarantee authorized access to the re-
sources. This includes protocols for authentication, access control, inferential
security, and integrity.
Isolation—methods to deal with a degraded network connection. This should
also include a means to work off-line if an intentional/unintentional disconnec-
tion has occurred. Furthermore, if the connection is too slow or unreliable to
work fully on-line, the user may intentionally choose to work off-line due to
bandwidth restrictions.
Semantic heterogeneity—methods to handle differences in representation, for-
mat, structure, conflict, and meaning among information sources and hence to
establish interoperability among different information sources. Techniques such
