Modeling Storing and Mining Moving Object Databases

1. Modeling Storing and Mining Moving Object Databases Proceedings of the International Database Engineering and Applications Symposium (IDEAS’04) Sotiris Brakatsoulas Dieter Pfoser Nectaria Tryfona Presentation by Michael J. Dudley

2. What is a Moving Object Database? • A Moving Object Database (MOD) consists of: • Spatial Data • Infrastructure information • Roads, Buildings, Obstructions, etc … • Non-spatial Data • Other thematic information • Trajectories • New area of research

3. Spacial and Non-spacial Data • Both scenarios are well explored research topics • Many DBMS allow for their manipulation.

4. Trajectories • New field of research • No commercial DBMS are available to manage the trajectory data

5. Handling Trajectories • Pre-process the data • Deal with errors in positional measurements • Data Modeling • Define a conceptual model to meet systems requirements • Data Storage • Logical data models, data types and query processing issues

6. What is a MOD use for? • Registering current information is not enough • A MOD must be able to extract further knowledge about a system • “Mini-World Fortune Teller”

7. ΙΧΝΗΛΑΤΗΣ System • ΙΧΝΗΛΑΤΗΣ means “Path Finder” in Greek • I will use the English translation when discussing this system • The Path Finder System(PFS) of Athens, Greece • Focuses on extracting further information about the movement of vehicles in the Athens municipal area. • Additional information about traffic conditions • Optimal routes • Prediction of troublesome situations

8. PFS History • PFS is a research project focusing on the development of a traffic management system • Two main goals • Registration of the semantics of moving object data in an object-oriented way resulting in a MOD • Adaptation of well known and widely used mining functions of characterization, clustering, and association in the moving object application domain and their expression through SML, allowing for a formal application in MOD

9. PFS Core Components • The Charateriser • Cluster Finder • Associator All three are used to perform data extraction on the MOD

10. Article vs. Presentation • Article • Section 2 – Organization of the database • Section 3 – Pre-processing, modeling and storage issues related to trajectory data • Section 4 – Architecture and components of the PFS • Section 5 – Analyses the mining process and presents the spatial mining language • Presentation • I will focus on Section 2 for the remainder of this presentation • Please contact me if you would like a full copy of this article.

11. Organizing the MOD • It is essential to study • the movement of objects • their properties and relations • Fundamental concept of movements of objects • After defining the semantics we organize them into a database, the MOD

12. The semantics of movement • Represent a moving object as point object • Volume and size do not play a critical role • This point object can be represented in a 3D graph • Space (x, y) • Time (t)

13. The semantics of movement • Need the moving object’s position on a continual basic • Current GPS and telecommunications technologies obtain position at discrete instances of time • By interpolating these samples we can extract the movement of the object • Linear interpolating takes the sample positions and makes them the ends points of line segments. The combination of the line segments makes an line in three-dimensional space

14. The semantics of movement The solid line below represents the movement of a point object. Space (x- and y-axes) and time (t-axis) are combined to form a 3D-area. Modeling Storing and Mining Moving Object Databases pg 3.

15. The semantics of movement The figure below shows a spatiotemporal space (the cube in solid lines) and several trajectories (the solid lines) contained in it. Time moves in the upward direction, and the top of the cube is the time of the most recent position. The wavy-dotted lines on top symbolize the growth of the cube with time. Modeling Storing and Mining Moving Object Databases pg 3.

16. The semantics of movement • In this study, the previous trajectory representation in three-dimensional space was chosen to be adequate to derive the properties and relationships of the object movement. • Answers both simple and complex questions • Which area did a vehicle cover during its trip? • Which vehicles left Athens after midnight moving East and were found close to each other 2 hours later?

17. The semantics of movement • Properties – based on requirements • The speed of the movement • The heading • The direction of the vehicle • The covered area • Indicating the area the vehicle covered during its trip • The traveled distance • The traveled time

18. The semantics of movement • Relationships • Relations between a trajectory and its spatial environment • Relations among trajectories

19. The semantics of movement • Relations between a trajectory and its spatial environment (trajectory/spatial) • Infrastructure elements • Roads, Buildings, Parks, etc … • Imaginary entities • City boundaries or query regions • In a temporal context these spatial entities become three-dimensional represented by a 3D region

20. The semantics of movement • Five basic spatial relationships • Stay Within • Bypass • Leave • Enter • Cross Modeling Storing and Mining Moving Object Databases pg 3.

21. The semantics of movement • Relations among trajectories (trajectory/trajectory) • Additional relevant to spatial relationship • Based on topological reasoning

22. The semantics of movement • Five common relations among trajectories • Intersect • Meet • Equal • Near • Far Modeling Storing and Mining Moving Object Databases pg 3.

23. The Database Schema of MOD • Previous concepts needs to be organized to define the data model of MOD • Use the class diagram of UML for the conceptual representation due to it’s popularity and high degree of comprehension and expressiveness.

24. The Database Schema of MOD Modeling Storing and Mining Moving Object Databases pg 4.

25. The Database Schema of MOD • Trajectory Class: • To capture a trajectory: • Trajectory ID • Vehicle ID • Position • Set of Operations • GetPosition • GetSpeed • GetTime • TravelledDistance • GetHeading Modeling Storing and Mining Moving Object Databases pg 4.

26. The Database Schema of MOD • 3D-region Class • Denotes the spatial environment of the trajectory • In this case it shows total covered area Modeling Storing and Mining Moving Object Databases pg 4.

27. The Database Schema of MOD • Trajectories have one or more relations with other trajectories or their 3D-region class. Modeling Storing and Mining Moving Object Databases pg 4.

28. The Database Schema of MOD • This style of representation has the advantage of describing two basic concepts • The trajectory of the moving object by keeping track of its movement • The moving object by recording its last known position

29. Questions • The road network of Athens, Greece Modeling Storing and Mining Moving Object Databases pg 5.