Chapter 5. Database Aspects of Location-Based Services Lee Myong Soo Mobile Data Engineering Lab. Dept. of Computer Science and Engineering, Korea University

Outline Introduction General Concepts Content Modeling Update Management Linear Referencing Conclusion

Introduction

Big challenge to data management posed by LBS. Transportation infrastructures must be represented in the databases underlying high-quality services. Several integrated representations capture different aspects of the same infrastructure.

General Concepts Content providers supply various type of content Weather data Traffic condition data, including information about accidents and congestion Information about sights and attractions Information about hotel rooms, cottages, and the like available for booking Information about the current locations of a population of service users

General Concepts Content Integrator Manages content received from multiple sources. Create and maintain a DB and IT infrastructure.

Classification of contents Geographic infrastructure( geocontent ) Geographic space itself, with hills, lake, rivers and etc Transportation infrastructure for cars, pedestrians, trains, aircraft, ships and etc. We focus on cars termed road networks. Users are interested in road distances, not Euclidean distances.

Classification of contents Real content ( business data ) Contain any content that may reference the geocontent Open-ended and extremely voluminous Examples Listing of movies currently running in the movie theater Seat availability information for the different shows Reviews of the movies Geocontent and real content need to be integrated.

challenges Dynamism of content How and when do update of content? Examples Road construction and accidents New stores open and existing stores close. The program of a movie theater changes. The sales available in a store change.

challenges Need for multiple representations infrastructure support different uses, including the following Content capture Content representation, update, and querying Route planning and way finding Display Representation integration

Content Modeling Internal Infrastructure Representation External Infrastructure Representation Kilometer post representation Graph representation Georeferences

Internal Infrastructure Representation Collection of linear elements and connection points Linear element Any kind of geographic feature to state location of point as a distance form start point.( e.g.,road, river, train track ) : records the linear elements Length – indicate the length of the element : capture connection Descriptive attributes – describe connection : relate element and connection Distance – from the start of element to the intersection element with connection

Kilometer Post Representation Used in connection with the capture of some content that is closely related to the roads. Specify the location of some geocontent relative to the nearest kilometer post on a specific road.

Content Modeling

Kilometer Post Representation : individual road parts :capture the kilometer posts for each road part

Kilometer Post Representation

Graph Representation An abstract view of an infrastructure that ignores geographic detail but preserves its topology. Used for connectivity-type queries, such as route guidance and way finding.

Graph Representation nodeID is unique within a representation But, a single primary key attibute, nID, is introduced for efficiency. Connect tow rows in the node table that have different nodeID and same representaionID. Length attribute indicates the length of the link. Relates links, and thus nodes, to elements. A link corresponds to only part of an element.

Geo-Representation Capture the geographic coordinates to the internal linear elements of the road infrastructure. Linear element is represented by collection of polyline. Polyline is a sequence of connected line segments. Line segment is given by a start and a end coordinate. Line segment polyline Linear element

Geo-Representation Capture the geographic coordinates of elements A low in this table references a linear element and represents a single line segment on that element Accuracy – capture the accuracy of the geographic descirption.

Content Modeling

Update Management Due to dynamic reality or supporting changed applications needs to support update. Update come in two guises Discrete change which is the conventional type of update Focus on update in the transportation infrastructure. Aspects that change continuously. Capture the continuously changing positions of moving users.

Update caused by discrete change Use dumb keys as primary keys. Dumb key carry no meaning in the modeled reality. If any content changes, you update in a single row. Otherwise, if primary key changed value, you update for each foreign key table.

Update caused by continuous change preferable to perform as few updates as possible Functioning in order to determine a required accuracy. For weather information, low-accuracy tracking will suffice. For list of the closest and friendly service users, much higher accuracy. A scenario which central server maintains a representation of a user’s movement.

Update caused by continuous change

Several possible representations of a user’s movement Constant function Update needed when user move a Euclidean distance out of threshold. Useful when the user is barely moving or moving within an area Linear function Update needed when user move unpredictably User send current position, speed and direction. Useful such as Cars traveling in a city environment

Update caused by continuous change Several possible representations of a user’s movement Utilize infrastructure Assume that the user is moving at constant speed along the linear element. Assume that the user stops when reaching the end of current segment. The route of the user Human move have a known destination. We tend to follow routes we have previously followed. Update occur because of incorrectly predicted speeds and route.

Client-Side Caching Scenario :Service to family on holiday might continuously display all nearby hotels, within a certain price range and whit rooms available as the family drives along. Underlying map is partitioned by means of a grid into small cells Update map grid cells

Linear Referencing Linear referencing is a natural and convenient means to associate attributes or events to locations or portions of a linear feature. The major advantage of linear referencing is its capability of locating attributes and events along a linear feature with only one parameter (usually known as measure) instead of two (such as latitude/longitude or x/y in Cartesian space).

Linear Referencing concepts Linear elements Locations are specifed along these objects. Meaningful start point and all point given by distance from the start point

Linear Referencing concepts Events: point, linear. Events occur along linear elements. Point event : traffic accident, roadside emergency phone, construction zone Linear event : speed limit, pavement type

Linear Referencing concepts Linear referencing method How a location along or beside a linear element is measured.

Conclusion The modeling of select aspects of reality as the foundation for the delivery of integrated, high- quality LBS. Relational data management technology is utilized for modeling. Future work Caching, transactions, concurrency control, recover, and access control.