Using Semantic Caching to Manage Location Dependent Data in Mobile Computing Qun Ren, Margaret H. Dunham Presented by Jekkin Shah

Objective Application of semantic caching to location dependent applications Eg. Mobile user, navigation system.

Contributions Mobility model to represent moving objects Formal definition of location dependent queries Strategies for query processing Cache management strategies

Modeling mobility L = (L X,, L Y ) location of object in 2D ( lat-long ) V = velocity at any instant of time L dt = ( (V X * dt +L X, ), (V Y *dt ) + L Y )

Query model (Q R, Q A, Q P, Q L, Q C ) Q L is the location Q C is the result of the query

Query predicate example (price < 100) ^ (L X – 20 < xposition < L X + 20 ) ^ (L Y – 20 < xposition < L Y + 20 ) a operator ( L X + c ) a = attribute, c = constant, L X = location variable

LDD Cache model Cache consists of LDD semantic segments Each segment starts with a new page Additional parameters like Timestamp is also stored

LDD query processing Query trimming –Probe query –Remainder query Coalesing partial results

LDD Cache Management FAR ( Farthest Away Replacement ) Improvisation on existing technique: Calculating Manhattan distance taking location and direction into account ( in-direction, out-direction )

Performance study Performance of semantic caching scheme Cache replacement strategy Workload Design Database design with various parameters Query design ( select only queries ) Moving path design –One-way, return trip, random