OMCAT: Optimal Maintenance of Continuous Queries' Answers on Trajectories
OMCAT is an extension of our previous work on Context-Aware
Maintenance of Continuous Queries(CAT), where CAT was a proof of
concept that triggers available in the commercial ORDBMS can be used
to maintain spatio-temporal range queries in MOD. However, in OMCAT,
we show the impact of different trigger semantic/context dimensions on
the efficient reevluation of continuous queries. We also show how the
query reevluation can be optimized by means of intra-query level
heuristics that utilize the spatio-temporal context information
embeded in the moving object trajectories, as well as the various
types of pending queries.
In Location-Based Services, it is desirable to maintain corrent answers to a set of pending continuous queries
efficiently. The functionality of query maintenance is provided by
the so-called Moving Object Database(MOD). In our settings, MOD stores the trajectories that describe the
motion of moving objects, which are pertaining to the future. It also
stores the various types of pending queries on the moving objects.
The queries considered include: static range query, dynamic within
distance query and dynamic k-nearest neighbor query. The database
also stores traffic abnormality that may affect the
planed motion of one or many moving objects, which may result in a
call for certain query reevaluation. These traffic abnormalities may be
reported on-line by various sources and have an immediate impact on the
pending query maintenance. When the database receives any traffic abnormality, our programmed triggers
tht monitor the pending query will fire to perform any necessary query
reevaluation. For a more serious treatment on our study of continuous query maintenance for trajectories, please
refer to , .
OMCAT demonstrates the process of query maintenance, from the moment a
traffic abnormality is reported to the system, to the time when all
query answers are brougt up-to-date again. 4000 trajectories are
pre-stored in the database, representing 4000 moving objects in the
urban area of city of Chicago. 9 continuous queries are also
pre-stored in the database to present the best demonstration effect.
However, the user is free to specify any query of its own. The user
can also specify a region of traffic abnormality with certain delay
effect. After OMCAT receives the user input, it sends this input to
the back-end database and performs query (re)evaluation. OMCAT then
receives the result from the database and update its presentation to
Figure 1 illustrate the architecture of OMCAT.
Figure 2 shows the main GUI interface of OMCAT.
Figure 3 is the screenshot after a user specifies certain query on the
Figure 4 shows the result after a user-specified traffic abnormality
is submitted to the database. The query answers are updated. Note
that the user can select the manner of query reevaluation, using
either the naive way or our optimized approach.
Instructions for downloading and running OMCAT
Our continuous query maintenance prototype is built on top of Oracle
Spatial, although it can be implemented for any
commercial database that supports User-Defined datatypes and
User-Defined functions, and use triggers or similar rule management
system to provide reactive behavior. The query maintenance logic and
programmed trigger are all implemented in PL/SQL and the source code
can be downloaded here.
To run our query maintenance system yourself, an Oracle Database of version 9i or
higher is required. To run OMCAT and see the visual effects, you will
also need to have Oracle Application Server Mapviewer installed.
Currently due to the limited computing resource, we do not provide
an on-line DEMO although one is possible. Interested visitor can
contact the author at: hdi117-AT-ece.northwestern.edu for further
1. Context-Aware Optimization of Continuous Range Queries Maintenance for
Trajectories, Goce Trajcevski, Hui Ding and Peter Scheuermann,
in Proceeding of MobiDE'05.
2. Context-Aware Optimization of Continuous Query Maintenance for
Trajectories, Hui Ding, Master's thesis, Northwestern
Your are the 's
visitor of OMCAT.