This presentation was done in June 2014 by one of our participants in ICST and ICBELSH conferences.

1. ACaching Scheme for Nearest-Neighbor
Queries in Mobile Database
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Presented By : Sandi Winn Aye

2. Outline
 Abstract
 Objectives
 Introduction
 Proposed System
 System Flow Chart
 Server Side
 Client Side
 Implementation
 Limitations of Proposed System
 Conclusion
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3. Abstract
 As the geographical position of a mobile user is becoming
more traceable, users need to pull data which are related to
their location.
 It is strongly recommended to minimize number of
connections and volume of data transmission from the servers.
 Caching data that are frequently accessed by mobile user in the
client side is an appropriate technique.
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4. Cont’d (Abstract)
 Most of the existing location services providers give more than
one nearest-neighbour queries results.
 In this system, a new caching scheme which is based on hybrid
and semantic caching is proposed.
 In server side, the kd-tree partition method is used to answer
nearest-neighbor queries.
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5. Objectives
 To get one only result nearest to the user current location
 To reduce the cache size by using hybrid caching
 To save the trips to the server by using semantic caching
 To minimize the search space by using kd-tree partition method in the
server side
 To get nearest neighbour result quickly and effectively by this partition
method
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6. Introduction
 The advances in wireless and mobile computing allow a
mobile user to perform a wide range of application although
there are some limitations in non-mobile hard wired
computing environments.
 Database applications are of special interest to us in mobile
computing environment.
 Database model in wireless devices are different from regular
client-server database.
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7. Cont’d (Introduction)
 There are many limitations such as frequent disconnection to
server, low power capabilities of these devices, etc. in the mobile
environment.
 Caching some of data which are frequently accessed by the user
in the client cache is a suitable solution.
 Resource-consuming caused by upstream queries and number of
trips made to the server can be reduced in this way.
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8. Proposed System
 Taking the advantages of caching scheme, this system offers the
query result to the users based on their current location quickly.
 Moreover, the connection and data transmission from the Database
server to the client can be reduced.
 The proposed system consists of two sides: sever side and client
side.
 As the pre-processing, the region for each data object is defined by
using adaptive-partition method in the server side.
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9. Cont’d (Proposed System)
 In the client side, the hybrid caching is combined with
semantic caching.
 The previous query answers are cached in the client system’s
cache according to the proposed caching’s policy.
 If there is a suitable answer corresponding to the user’s query
in the client’s cache, this query can be answered from that
cache without connecting to the server.
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10. Flow Chart of Proposed System
User’s location and
Query?
Start
Is there query
cache?
Display Result
End
Cache’s
DB
Retrieving Data From
Client’ cache
Nearest Neighbor
data object
Processing in Server Server’s DB
Storing query result
in Cache’s DB
no
yes
Checking to Cache’s
DB for query result
result in client’s
Client
Side
Server
Side
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11. Server Side
 In the server side, the search space is divided by using kd-
tree partition method.
 It recursively partitions the search space into two
complementary subspace such that the number of objects
associated with the two subspaces is nearly the same.
 The space is partitioned horizontally or vertically.
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12. Cont’d (Server Side)
 Split the point set alternatingly by x-coordinate and by y-
coordinate.
 split by x-coordinate: split by a vertical line that has half the points
left and half right.
 split by y-coordinate: split by a horizontal line that has half the
points below and half above.
 Each internal node stores the splitting node along x (or y).
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13. Cont’d (Server Side)
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14. Cont’d(Server Side)
Nearest-Neighbor Search
 Starting with the root node, the algorithm moves down the tree
recursively.
 (i.e. it goes right or left depending on whether the point is
greater or less than the current node in the split dimension).
 Once the algorithm reaches a leaf node, it saves that node
point as the "current best“.
 The algorithm unwinds the recursion of the tree, performing
the following steps at each node.
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15. Client Side
 As there are limitations in the wireless environment, it is strongly
recommended to save the trip to the server.
 Caching seems to be profitable in such situations.
 Caching the previous nearest object in client system’s cache will be
applicable for the forthcoming queries.
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16. Cont’d (Client Side)
 All previous nearest objects can’t be cached in client’s cache
because of limited size of the cache.
 It needs to cache some of the objects that are frequently accessed
by database applications.
 In the proposed caching scheme, there are two types of caching:
hybrid caching and semantic caching.
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17. Hybrid Caching
 Hybrid caching is a mix of object caching and attribute
caching.
 In object caching, it stores an object that is frequently
requested by the mobile user.
 All attributes of this object are cached in the client side.
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18. Cont’d (Hybrid Caching)
 This not only wastes the transmission bandwidth, but also
occupies storage for caching other more frequently
accessed attributes.
 In the attribute caching, it cache attributes of this object
that is mostly accessed.
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19. Semantic Caching
 The semantic description and results of previous query results are
stored in the mobile client cache.
 By using semantic caching, a query can be partially answered from
the client cache if a query isn’t an exact match.
 Then the original query is trimmed and the trimmed part is sent to
the server and processed there.
 The amount of connection and data transmission to the server can
be reduced by processing queries according to this caching.
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20. Cont’d (Semantic Caching)
 The semantic description contains object name, attribute set, the
location of client that is described by x, y coordinate as
<SO,SA,PX,PY>.
 This semantic description is as shown in the table.
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SO SA PX PY
hotel street 10 30
hotel street,tel 20 40
restaurant street 50 60
restaurant cuisine 70 80
hotel tel 55 66

21. Cont’d (Semantic Caching)
 By trimming queries, previous results in the client cache
can be partially used if the query is not an exact match.
 The communication cost from client to server can be
reduced.
 Only select and project queries can be applied.
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22. Implementation
There are possible conditions according to user current location.
• If a new query is totally answered from the client cache,
communication to the server is unnecessary.
• If a new query doesn’t exactly match the one from the client cache,
it needs to connect with the server.
• By using semantic caching, a query can be partially answered from
the client cache in above condition.
• The original query is trimmed and the trimmed part is sent to the
server and processed there.
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23. Cont’d(Implementation)
• The amount of data transmission to the server can be
reduced by processing queries according to this caching.
• Main advantage of semantic caching is that by trimming
queries, previous results in the client cache can be used if
the query is not an exact match.
• Moreover, the communication from client to server can
be reduced.
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24. Cont’d(Implementation)
 The user can get her current location which is shown as latitude
and longitude from GPS.
 There are seven services in this proposed system.
 Moreover, there are some attributes related to each service.
 Firstly, one service and some attributes which she wants to find
nearest one to her current location can be chosen.
 After getting her location and choosing one service and its
attributes, the system checks the client’s cache base on her current
position to see whether the query answer is available.
 If there is a suitable cache record corresponding to the location of
the user, the most appropriate answer is retrieved from the cache
and this answer can be returned to the mobile user quickly.
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25. Cont’d(Implementation)
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26. Cont’d(Implementation)
 Otherwise, the current
location of the user and
query are transmitted to
the server.
 The server finds one
nearest neighbor object
and its attributes
according to the user’s
current location and
sends back one nearest
neighbor object to the
user. 26

27. Cont’d(Implementation)
• When data is sent by the client, only one nearest-neighbor
result is computed in the server as follows:
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28. Conclusion
 In this system, the location-based application that
provides only one nearest neighbour based on user
current location has been proposed.
 To overcome limitations in the mobile environment, this
system presents that data caching is a profitable solution.
 A new caching scheme is proposed to find only one
nearest neighbour result and its related attributes based on
user current position.
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29. Cont’d (Conclusion)
 Hybrid caching and semantic caching are used by the proposed
system for reducing wireless data transmission and cache size.
 KD-tree partition index is used in the server side to answer
queries for finding the nearest services facilities based on
mobile client’s locations more accurately.
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