Modeling Storing and Mining Moving Object
DatabasesProceedings of the International Database Engineering and Applications Symposium
(IDEAS’04)
Sotiris BrakatsoulasDieter Pfoser
Nectaria Tryfona
Presentation byMichael J. Dudley
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
Spacial and Non-spacial Data
Both scenarios are well explored research topics
Many DBMS allow for their manipulation.
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
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”
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
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
PFS Core Components
The Charateriser Cluster Finder Associator
All three are used to perform data extraction on the MOD
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.
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
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)
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
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.
The semantics of movementThe 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.
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?
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
The semantics of movement
Relationships Relations between a trajectory and its
spatial environment Relations among trajectories
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
Five basic spatial relationships Stay Within Bypass Leave Enter Cross
The semantics of movement
Modeling Storing and Mining Moving Object Databases pg 3.
The semantics of movement
Relations among trajectories (trajectory/trajectory) Additional relevant to spatial relationship Based on topological reasoning
The semantics of movement
Five common relations among trajectories Intersect Meet Equal Near Far
Modeling Storing and Mining Moving Object Databases pg 3.
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.
Trajectory Class: To capture a trajectory:
Trajectory ID Vehicle ID Position
Set of Operations GetPosition GetSpeed GetTime TravelledDistance GetHeading
The Database Schema of MOD
Modeling Storing and Mining Moving Object Databases pg 4.
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.
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.
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