Data Management for Mobile Computing

The emerging technology of cellular communications, wireless Lan and data network and satellite service allow mobile user to access information anywhere and anytime through equipment like palmtop, laptop and PDA (personal digital assistant). In coming year, this technology will pose challenging problem to the database community.

What problem ?

Mobility - Reasearch issues

Locating Users

Locating users who are on the move at all time is unrealistic and unnecessary. The user's location stored in the database will not be the latest updated location. Therefore, search (paging) over some limited areas (zone) have to be applied. The use of a general search process which is a combination of a database lookup and paging (additional communication) will be explained later.

Queries on location dependent data

Use of query to perform search such as "where is the nearest doctor" or "find the shortest route to the hosiptal". If database's location information is not accurate, a combination of database search and additional data acquisition during run time of the query is necessary.

Replicating Information

Replication means the way the system ensures transparency for mobile users. When a user moves to a new location, he would like to have his environment to be recreated at the new location. To maintain performance transparency, a migration of the state variable representing the ongoing process from one machine to another or establish a new replica. Hence, mobile environment requires dynamic replication schemes that replicate data on the basis of changing "centers of activity".

Disconnection - Reasearch issues

Total disconnection occurs when user switched off to save power or during relocation. Besides this, we have to differentiate various degrees of connection so that we are able to determine what disconnection protocol to be used.

Cache Consistency

If the mobile user has cached a portion of the shared database, he may request different level of cache consistency. At what level of consistency depends very much on the type of connection as each type of connection may have a different degree of cache consistency associate with it.

Hand Off and recovery

When the user moves or switches off in the middle of a transaction's execution, the mobile user should give instructions to the local host on completing the executed transaction. What type of approach to adopted? For total disconnection, CODA use optimistic methods. For weak or elective disconnection, it depends on several factors such as connection cost (bandwidth), power restriction and availability of resources on the mobile.

New Access Methods - Research Issues

New access methods motivated by wireless transmission medium and by power restrictions on palmtop. Hence, this warrants new solutions.

Wireless Medium

Since cost of broadcasting over the wireless does not depend on the number of users who are listening, wireless medium provides an excellent platform for broadcasting information to a massive number of user. Examples of queries repetitively by large number of users in local area are traffic information, stock market data, local sales events, new services. Broadcasting is more economical in terms of transmission cost.

Energy Efficient Data Management

Limited battery lifetime has led to a restricted use of energy resources. This a major factor to consider for efficient data management. The following is a list of factor to be consider.

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