Chapter 5. Database Aspects of Location-Based Services

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Chapter 5. Database Aspects of Location-Based
Services
Lee Myong Soo lms9711_at_korea.ac.kr http//mobide.k
orea.ac.kr Mobile Data Engineering Lab. Dept. of
Computer Science and Engineering, Korea
University
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Outline

• Introduction
• General Concepts
• Content Modeling
• Update Management
• Linear Referencing
• Conclusion

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Introduction
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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.

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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

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General Concepts

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

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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.

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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.

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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.

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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

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Content Modeling

• Internal Infrastructure Representation
• External Infrastructure Representation
• Kilometer post representation
• Graph representation
• Georeferences

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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
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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.

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Content Modeling
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Kilometer Post Representation
individual road parts capture the
kilometer posts for each road part
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Kilometer Post Representation
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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.

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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.
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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
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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.
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Content Modeling
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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.

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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.

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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 users movement.

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Update caused by continuous change
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Update caused by continuous change

• Several possible representations of a users
  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

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Update caused by continuous change

• Several possible representations of a users
  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.

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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
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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).

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Linear Referencing concepts

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

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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

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Linear Referencing concepts

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

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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.