Download “UNDERSTANDING CAPABILITIES OF SPATIAL DATABASE

“UNDERSTANDING CAPABILITIES OF SPATIAL DATABASE
(POSTGIS) IN DISTRIBUTED ENVIRONMENT”
MID TERM REPORT
Submitted in Partial Fulfilment for the Award of
M.Tech in Computer Science
Of
Banasthali University, Rajasthan
Supervisor:
Submitted By:
Prof. N.L.SARDA
MONIKA YADAV
Computer Science & Engg Dept.
11768
IIT BOMBAY
AIM & ACT
Banasthali University (Rajasthan)
2011-2012
DECLARATION
I hereby declare that the project entitled “Understanding capabilities of spatial database
(PostGIS) in distributed environment” submitted for the M.Tech Degree is my original
work and the project has not formed the basis for the award of any degree, associate ship,
fellowship or any other similar titles.
Signature of the Student:
Place:
Date:
ACKNOWLEDGEMENT
The partial completion of this Internship project was possible with the help and guidance that I got from my
Professor N.L.Sarda and Dr. Smita Sengupta at GISE Lab. I take this opportunity to thank them all for their
cooperation extended to me during my internship specially Mr. Bharat Singhvi, Mr. Nikhil Morajkar and
Ms. Anuja Shukla. I also take this opportunity to specially thank Prof. N L Sarda for his guidance and kind
co‐operation rendered throughout my internship. His insights, expertise and energy contributed greatly to the
success of this internship. I also thank my parents who always supported me in all aspects. Formal and
informal discussions with Neha Arora, Bharti Kathpalia and Mr. Kashiram Vichare also helped me in
achieving various tasks.
Finally, I thank Banasthali University for giving me this opportunity to work at a great place and in a great
lab and laying the Foundation for my future career path.
Monika Yadav,
Intern,
Geo-Spatial Information Science & Engineering (GISE),
Advance Research Lab,
Indian Institute of Technology Bombay(IITB)
M.TECH, Banasthali University (Rajasthan)
TABLE OF CONTENTS
CHAPTER NO.
1.
TITLE
ABSTRACT
INTRODUCTION
1.1 Objective
1.2 Technology Used
1.3 Target Users
2.
LITERATURE REVIEW
2.1 Study of PostGIS
2.2 Benchmarking On Spatial Database for Single User.
2.3 Pgpool-11-3.04: Tool for parallel processing in Postgresql.
2.4 Join Processing in Multi Database System.
3.
OUR APPROACH
3.1 Data Partition
3.1.1 Bounding Box Wise.
3.1.2 Feature wise.
3.2 Block Diagram of our approach
3.3 Query Fragmentation.
3.4 Query Redirection to Distributed Database.
3.5 Query Execution and Storage of result
3.6 Displaying Result on Geoserver.
4.
CONCLUSION
5.
FUTURE SCOPE
6.
REFERENCES
ABSTRACT
Many Organisations like Municipal Corporation and E-Governess has large scale data stored in Distributed
Database (Postgresql-8.4). In order to achieve this I have designed a java application which will query the
remotely distributed databases. In this application user will enter the query that will further get fragmented
into two parts if query is on more than one table .Then part of query will goes to the one server and another
part of query will goes to the another server and get executed on remote server.
Now transfer of Result set from both remote servers to Local host take place and then union of result set or
any operation that require data from both server take place on local host.
Finally we will populate Combination of result from both servers on Geoserver.
1. INTRODUCTION
1.1 Objective:
To design a Java application in order to implement the concept of distributed databases by taking
spatial database (PostGIS) in order to achieve performance optimization. I have been involved in
research in parallel and distributed computing systems. I studied various problems in distributed
systems and distributed databases and my work is on PostGIS which is a spatial Database.
My project work includes designing of a Java application which will provide User Interface for
querying Distributed Database (PostGIS), connection establishment to Remote Postgresql Servers,
retrieving combined result from remote servers and populating final result on Geoserver.
1.2 Technology Used:
Database:

Postgresql -8.4: PostgreSQL is an Open
source object-relational database management system (ORDBMS) [4].

PostGIS-1.5.2: PostGIS is an extension to the
PostgreSQL object-relational database system which allows GIS (Geographic Information
Systems) objects to be stored in the database. PostGIS includes support for GiST-based R-Tree
spatial indexes, and functions for analysis and processing of GIS objects [9].

IIT-Bombay Database: IIT-Bombay database consisting
of geographical information of IIT-Bombay. We have relational data named
Builtup,Boundary,Bus_stop,campus_boundary,culvert,Location_plan,open_space,places,revenue
_boundary,zone, gate and all utilities (electrical line, roads, sewerage lines, water lines, telephone
lines) etc. For my experiment purpose I have taken IIT-B data only.
Programming languages:

JAVA EE: Java Enterprise Edition is a programming platform—
part of the Java Platform-for developing and running distributed multi-tier architecture Java
applications, based largely on modular software components running on an application server.

JavaScript: A client side scripting language used to create dynamic web
content and user interface.

Java Servlet: A servlet is a Java programming language class used to extend the
capabilities of servers that host applications accessed via a request-response programming model.
Although servlets can respond to any type of request, they are commonly used to extend the
applications hosted by Web servers

Java Server Pages (JSP): Java Server Pages (JSP) technology provides a simplified, fast
way to create dynamic web content. JSP technology enables rapid development of web-based
applications that are server and platform independent.
Tools & Development Environment:
 Apache Tomcat 6.0.18 Server: Apache Tomcat is a Servlet container developed by the Apache
Software Foundation (ASF). Tomcat implements the Java Servlet and the Java Server Pages
(JSP) specifications from Sun Microsystems, and provides a "pure Java" HTTP web server
environment for Java code to run.
 ECLIPSE J2EE: Eclipse is a toolkit which is designed for the creation of complex projects,
providing fully dynamic web application utilizing EJB’s. This consist of EJB tools , CMP ,data
mapping tools & a universal test client that is designed to aid testing of EJB’s.
 Pgadmin-III: PgAdmin is the most popular and feature rich Open Source administration and
development platform for Postgresql which is the most advanced Open Source database.
PgAdmin is designed to answer the needs of all users, from writing simple SQL queries to
developing complex databases. The graphical interface supports all PostgreSQL features and
makes administration easy.
 Geoserver (Any OGC complaint server): GeoServer is an open source software server written
in Java that allows users to share and edit geospatial data. Designed for interoperability, it
publishes data from any major spatial data source using open standards. Any OGC complaint
server is used to deploy my web application [12] [13].
1.3. TARGET USERS:
This application is helpful in those areas where large scale data is used and we need performance
optimization while accessing data from different Databases distributed remotely.
Presently in many organisations we need to keep the data in different databases in multiple servers
because of huge amount of data. We need some mechanism in order to access the data from different
sites .My project work includes finding such a capability in PostgreSql-8.4 and it is useful in any
Organisation like E-Governess ,municipal corporation in order to fire query on distributed Database
and in order achieve optimization of performance.
2. LITERATURE REVIEW
2.1 Study of PostGIS[9]:
Features Capacities of PostGIS:
1.
2.
3.
4.
5.
6.
7.
8.
Capacity known : up to 32 TB data
Supports OGC Standards
It has proj4 Cartographic projection Library
GEOS-Geometry Engine Open Source-Provide Spatial predicate functions, Spatial Operators
and topological functions
Huge Client/Server Library Support
Advanced indexing.
Transformation Support
Variety of output format options ((E)WKT,(E)WKB,GeoJSON,GML,KML,SVG
Limitation of PostGIS:
1. Not multiprocess(Base application PostgreSQL is multiprocess enabled except for Iowaits but
the extension PostGIS is not multiprocess)
2. No true Geodetic Support.
3. Fewer hosting provider than Oracle/MYSQL Server/MYSQL
2.2 Benchmarking On Spatial Database for Single User [14].
In order to understand the capabilities of postgres-8.4 and Postgis-1.5.2 I have studied the
experiment done on spatial database for Single user by Subham Roy (student at IIT-Bombay).
Brief of the Experiment:
Comparison of Open-source and Proprietary products:
Experiment has two parts: Cold Start: Each query is being run freshly by clearing all the buffer cache pages.
 Warm Start: A bunch of related queries is run to measure the performances of the two
databases.
Ways of Benchmarking:
Functional Benchmarking: Test Functionality supported by the Spatial Database
Performance Benchmarking: Test Speed of the Spatial Database
Database Benchmarking: Test performance and throughput of Spatial Database
Brief of experiment done By Subham Roy:
He has taken Oracle11g on Windows7 and Postgres 9.04/Postgis 1.5.2 on Ubuntu 10.04 for
benchmarking with keeping all system requirement same for Oracle and PostGIS using 2010
TIGER/LINE DATA.
By running many spatial queries(Some simple query and some Complex query)..He get to know that
postgresql has better performance as compare to Oracle. For all queries (simple and complex) time
taken by Postgresql is less and Postgres uses the underlying GEOS(Geometry Engine - Open Source)
library functions for implementing the geometric operations whereas Oracle 11g implements them on
its own. So for Single User majority Postgres performs well.
2.3 Pgpool-11-3.04: Tool for supporting distributed database concept in
Postgresql:

PgpoolAdmin: The pgpool Administration Tool is management interface for pgpool to
monitor, start, stop pgpool and change setting for pgpool.
I am using PgpoolAdmin-3.0.3 which is suitable of all pgpool-II-3.0 version (I was using PgpoolII-3.0.4) [7]
Fig: 1 Pgpool Admin
Pgpool-II-3.0.4:
pgpool-II is a middleware that works between PostgreSQL servers and a PostgreSQL database client.
It is licensed under BSD license [5].
Feature of pgpool of our interest:
Parallel Query:
Using the parallel query function, data can be divided among the multiple servers, so that a query can
be executed on all the servers concurrently to reduce the overall execution time. Parallel query works
the best when searching large-scale data [6]
Structure of working of Pgpool:
Pgpool-II-3.0.4
Rs=Rs1 op Rs2
Server 3 or Local Host
Q
Dblink.sql
System_db
Rs1
Q
Rs2
Server 1
Server 2
Fig: 2 Structure of working of pgpool
Annotations Used in Diagram:
Q- Sql Query
Rs1-Result Set stores result after execution of Query Q1
Rs2-Result Set stores result after execution of Query Q2
Rs-Spatial function of Rs1 and Rs2.
Op-operation applied on rs1 and rs2 either intersection, union, difference etc.
Pgpool-II-3.0.4-Tool for Parallel Query Processing


Systemdb:User defined rules for data partitioning and merging of result via Dblink
Dblink.sql: Its Sql file in usr/local/postgresql/contrib.dblink.sql.It is used to query local
Postgresql and remote Postgresql [8].
Disadvantage of dblink:
1. It lacks SQL server’s linked server approach or open query that allows for synchronized join
between linked servers/databases.
2. Not useful in cases where you need to join lots of data with local data.
3. Need to specify output structure.
Description of working of pgpool: Pgpool distributes the data on both the server and then redirect
same query on both the server and get the combination of result via dblink.sql.
Reason for dropping Pgpool:
Pgpool is not suitable for our desire task because it only redirects the same query to both server and it
does not support query fragmentation.
2.4 Join Processing in Multi Database System[14].
Description of Experiment:
User will input the query that will change into modified query. Modified query will separate the
Local and remote references according to qualification. Then part of query get executed on local
server and part of query get executed on HP-SQL remote server and then transferring of some
component from remote server to local server take place because in order to perform join both
relations involved in the join need to be present at the same site before join operation take place.
I have used the same idea in my Java application considering both databases as postgreSQL-8.4.
Structure Used for Join Processing in Multi database system:
Remote
References
Local Database
Copy some
component to local
Separate Local
machine in order to
references and remote
perform join
references from Modified Query
Query
Multi Database Support Layer
Remote
Database
Quer
y
Fig: 3 Join Processing in Multi database system
3. OUR APPROACH:
3.1 Database Partition:
I have used two methods for Data Partition: Bounding Box wise partition and Feature wise partition.
3.1.1. Bounding Box wise Partition:
Bounding Box: The bounding box is described by 4 numbers; the x-y coordinates of the lower-left
corner of the image, followed by the x-y coordinates of the upper-right corner of the image.
Representation of Bounding Box:
BBox (Xmin, Ymin, Xmax, Ymax).
Method used for partitioning data Bounding Box wise:
Bounding Box of IIT-Bombay is:BBox (72.902, 19.122, 72.911, 19.142)
By knowing Bounding Box of IIT-B, we have divided the whole data in two Polygons.
Polygon1= (72.911 19.122, 72.911 19.122, 72.911 19.142, 72.902 19.142, 72.902 19.122)
Polygon2= (72.902 19.122, 72.911 19.122, 72.911 19.142, 72.902 19.142, 72.90219.122)
Then by applying SQL Query we have find out Intersection of each Layer with both polygon. Layer
intersecting one Polygon is taken in one server and layer intersecting other polygon is taken in
another Server.
SQL Query for finding out whether one layer (e.g. electric_line) intersecting Polygon1 and Storing
result in a table (e.g. electric_line) for partition 1:
SELECT ST_Intersects (electric_line.the_geom, ST_GeomFromText ('POLYGON ((72.902
19.122, 72.911 19.122, 72.911 19.142, 72.902 19.142, 72.90219.122))' , 4326)),* INTO
gis_schema.electric_line_P1 FROM gis_schema.electric_line ;
SQL Query for finding out whether one layer (e.g. electric_line) intersecting Polygon2 and Storing
result in a table (e.g. electric_line) for partition 2:
SELECT ST_Intersects (electric_line.the_geom, ST_GeomFromText (‘POLYGON ((72.911
19.122, 72.92 19.122, 72.92 19.142, 72.911 19.142, 72.911 19.122))’, 4326)),* INTO
gis_schema.electric_line_P1 FROM gis_schema.electric_line ;
Likewise we perform the query for all features or all layers and divide the data into 2 and the data
which lies on boundary we are replicating that data on both servers.
For finding out data that lies on Boundary of two Polygons, we will apply following SQL Query:
SELECT count (*) FROM gis_schema.builtup_p1 as p1 JOIN gis_schema.builtup_p2 as p2 ON
p1.gid = p2.gid where p1.st_intersects=p2.st_intersects;
Table showing no of rows that lies on Boundary:
Original Table
boundary
Builtup
Bus_stop
Campus_boundary
Cmp_boundary
Culvert
Electric_line
Electrical_assest
Gate
Location_plan
Open_space
Open_spacev2
Places
Proposed_building
Proposed_road_edg
e
Revenue_boundary
Road_centerline
Road_edge
Road_junction
Sewerage_assest
Sewerage_line
Swd_bedlevel
Swd_centerline
Swd_edge
Partition 1
Boundary_bb1
Builtup_bb1
Bus_stop_bb1
Campus_boundary_bb1
Cmp_boundary_bb1
Culvert_bb1
Electric_line_bb1
Electrical_assest_bb1
Gate_bb1
Location_plan_bb1
Open_space_bb1
Open_spacev2_bb1
Places_bb1
Proposed_building_bb1
Proposed_road_edge_b
b1
Revenue_boundary_bb
1
Road_centerline_bb1
Road_edge_bb1
Road_junction_bb1
Sewerage_assest_bb1
Sewerage_line_bb1
Swd_bedlevel_bb1
Swd_centerline_bb1
Swd_edge_bb1
Partition 2
Boundary_bb2
Builtup_bb2
Bus_stop_bb2
Campus_boundary_bb2
Cmp_boundary_bb2
Culvert_bb2
Electric_line_bb2
Electrical_assest_bb2
Gate_bb2
Location_plan_bb2
Open_space_bb2
Open_spacev2_bb2
Places_bb2
Proposed_building_bb2
Proposed_road_edge_bb2
No. of rows lies
at Boundary
12
6
0
1
5
1
16
7
8
3
7
7
0
0
12
Revenue_boundary_bb2
5
Road_centerline_bb2
Road_edge_bb2
Road_junction_bb2
Sewerage_assest_bb2
Sewerage_line_bb2
Swd_bedlevel_bb2
Swd_centerline_bb2
Swd_edge_bb2
12
8
2
0
11
0
4
7
Telephone_assest
Telephone_line
Water_assest
Water_body
Water_line
zone
Telephone_assest_bb1
Telephone_line_bb1
Water_assest_bb1
Water_body_bb1
Water_line_bb1
Zone_bb1
Telephone_assest_bb2
Telephone_line_bb2
Water_assest_bb2
Water_body_bb2
Water_line_bb2
Zone_bb2
0
8
1
0
13
4
3.1.2. Feature wise partition:
For feature wise partition I have stored all utilities on one server and all other feature on another
server.
For feature wise partition I have stored the different table on different servers because a table in one
Postgresql is equivalent to one feature.
Features stored on Server 1
Boundary
Builtup
Bus_stop
Campus_boundary
Cmp_boundary
Culvert
Gate
Location_plan
Open_space
Open_spacev2
Places
Proposed_building
Proposed_road_edge
Revenue_boundary
Road_centerline
Road_edge
Road_junction
Zone
Features stored on Server 2
Electric_line
Electrical_assest
Sewerage_assest
Sewerage_line
Swd_bedlevel
Swd_centerline
Swd_edge
Telephone_assest
Telephone_line
Water_assest
Water_body
----------------------------------------------------------------
3.2 Structure of our approach
Display of result
Join and Other
operation require
data from both
servers performed at
Local host
Result set of
Q2
Result set of
Q1
Query(Q1)
Query(Q2)
Execution of
query Q1
Execution of
query Q2
.
Remote Server 1
Remote Server 2
Fig: 4 Structure of working of java application
Description of Structure:
Method mentioned under section 3.3, 3.4 and 3.5
3.3. Query Fragmentation:
Query fragmentation includes division of query into two partitions so that part of query will goes to
one server and part of query will goes to another server.
For Fragmentation of query I have designed a java application that includes the following:
SQL Parsing: Parsing of SQL statement is done by “String Tokenizer” method in java and various
conditions are applied in order to consider all cases entered by user.
By keeping in mind all cases entered by user, a java application is designed in which all field name
referring to one server are kept under one part of query and all other field name.
Operator Tree: operator tree defines a partial in which operations must be applied in order to
produce the result of query. leaves of a tree represent relations on different server.
I have used idea of operator tree in order to translate the global query into fragmented one and then
applying operation in a sequence by considering local optimization in mind.
Bounding Box wise partition: In bounding Box wise partition we need not to fragment the query
because all table names are same only size differs.
Feature wise partition: in feature wise partition we need not fragment the Query and query
fragmentation is done by above mentioned method.
3.4. Query Redirection to Distributed Databases:
For Query redirection to distributed databases I have followed below mentioned
methology:
By distributed database we mean two different servers in which partitions of database are stored and
from a third server let’s say Local Host we will Query the both remote servers containing
partitioned data.
LookUp Table:
A Lookup Table containing Meta information i.e. which table is stored on which server together with
their Credential (Host, Username, password, port) is maintained at Local Host. From lookup table we
can redirect our query to that particular server on which the data query asking for resides.
Screenshot of lookup table stored in Pgadmin3at local host or on 3rd server for feature wise partition:
Fig: 5 lookup table at local host
 Extracting ServerName from LookUp table At Localhost for Both part of Query.Now
Redirecting part of Query to one server (By Establishing Connection to that server by
fetching parameter from LookUp Table) and Part of Query to another Server.
3.5. Query Execution and Storage of result:
A Java code will do the following:
 A part of query gets executed on one server and another part of Query gets executed on
another Server. We Obtain result in the form of Result set .Let say Resultset1 and Resultset2.
 Now transferring of result-set from Remote Server is done with the help of Local host
server's Object by creating a table (which is mentioned by User in Query)or executing the
create Sql query with the help of statement object of Local host. likewise do for Result set
from another server.
 Now we obtain two table which contains result of User Query from server1 and from server
2.Now we can apply any Operation which contains data from both Table and we can perform
Join.
 Then we will store the final Result in 3rd table (Drop the table if already Exists )
3.6.
Java
Application developed till now:
Step1:
User will enter the Query either for Single table or for more than one table and click on Get Result
button.
For querying more than one table we need to do Query Fragmentation and I am working on that.
Screenshot for user querying on single table:
Fig: 6
Form
asking User’s query
Step 2:
Click on Get Result Button:
On click Event of Get Result following Task will take place (via Java Code):





Connection to all three servers that is Local Host ,Server1 and Server2 is made.
Query will go to both server and get executed there .
By the use String Tokenization getting table name from Query.
If table already exist then drop it otherwise create it.
Storing combination of result from server1 and server2 in that table in postGIS on 3rd
i.e. Local Host.
I am also displaying the combination of result from both Servers in Console.
Server
Fig: 7 After click on Get Result button
Step3:
A Table get created in PostGIS on Local Host which is combination of result from both the server
Fig: 8
Stored
Table
at
Local
host In
PgAdm
in3
3.5.
Displaying Result on Geoserver:
Steps to display result on Geoserver or displaying 3rd table which is obtained as combined result
from both server:-
Step 1:
Start the Geoserver-2.1 by typing following command in terminal:
$ sh geo.sh (geo.sh is startup file for geoserver )
Step 2:
Go to the browser and type the URL:http://localhost:18080/geoserver/web/
A screen will appear then enter username and password for Geoserver.
By default username and paaword for geoserver is:
Username: admin
Password: geoserver
Click on login and now geoserver is ready for further operation:
Fig: 9 Geoserver Login
Step 3: Creation of workspace inside Geoserver:
Fig:
Click
10.1
on
workspace
Now click on Add new workspace
Fig: 10.2 Add New Workspace
Enter
of
name
workspace and Namespace URI and then click on submit.
Fig: 10.3 Enter Name and Namespace URI
After click on submit a workspace get created and we can search for our namespace by typing its
name in search
Fig: 10.4 Workspace get created
Step 4: Creation of Store inside Geoserver
Fig: 11.1 Click on Stores
Fig: 11.2 Click on Add new store
Fig: 11.3 Click On PostGIS
All Layers which are Stored in Database in pgadmin3 get Displayed here. Which shows connection
of Geoserver to PostGIS
Fig: 11.4 Enter basic Information for connection to PostGIS
Ste
p 5:
Publ
ishi
ng
Post
GIS
laye
r On
Geo
serv
er:
Fig:
12.1
Clic
k On
Publish
Enter the information require to connect postGIS to geoserver.
Fig: 12.2 Select Coordinate System & Compute min, max coordinates from data
Fig: 12.3 Click on layer Preview
Fig: 12.4 Search for Layer and click on Open Layers
Layer from PostGIS storing combined Result from both servers can be viewed as a map on
Geoserver.
Fig: 12.5 Map view of layer from PostGIS On geoserver.
CONCLUSION
The Java application designed can be used by many Organisations having large scale of data distributed over
different servers and by implementation of Query Fragmentation and only transferring of Result set rather
than whole data results in performance gain.
It will solve overhead of data having only at one site and it will also result in distribution of load on one
server only.
Partial achievement of design of application has implementation of Query on single table.
At the end my application will include query on multiple tables or implementation of Query Fragmentation.
FUTURE SCOPE
Parallel database systems attempt to exploit recent multiprocessor computer architectures in order to build
high-performance and high-availability database servers at a much lower price than equivalent mainframe
computers.
Presently in many organisations we need to keep the data in different databases in multiple servers because
of huge amount of data. We need some mechanism in order to access the data from different sites. Scope of
this application is in those areas where large scale data is used and we need performance optimization while
accessing data from different Databases distributed remotely.
My project work is useful in any Organisation like E-Governess, Municipal Corporation in order to fire
query on distributed Database (Postgresql-8.4) and in order achieve optimization of performance.
REFERENCES
[1] Stefano Ceri, Giuseppe Pelagatti , “ Levels of Distributed Transparency, Distributed Database
Design, Translation of Global Query to Fragment Query,” in Distributed Databases: Principles and
Systems, pg-37-126.
[2] S. Bandyopadhyay, “Join processing in a Multi database system” in Data Management (New
Dimensions and Perspectives).
[3] P.Bernstein N.Goodman E.Wong ,C.Reeve and J.Rothnie, “Query Processing
in a System for Distributed Databases ”.
[4] “Postgresql”, Available: http://www.postgresql.org/
[5] “Features of pgpool”, Available: http://pgpool.projects.postgresql.org/
[6] “Pgpool tutorial”, Available: http://pgpool.projects.postgresql.org/pgpool-II/doc/tutorial-en.html.
[7] “PgpoolAdmin features and installation,
Available:http://pgpool.projects.postgresql.org/pgpoolAdmin/doc/en/install.html
[8] “Dblink description”,
Available: http://www.postgresonline.com/journal/archives/44-Using-DbLink-to-access-otherPostgreSQL-Databases-and-Servers.html
[9] PostGIS 1.5.2SVN Manual.
[10] “PostGIS Reference”, Available: http://postgis.refractions.net/documentation/manual-1.3/ch06.html
[11] “Spatial Functions”, Available: http://postgis.refractions.net/docs/ST_Intersects.html
[12] “Geoserver-2.1 User Manual”, Available: http://docs.geoserver.org/stable/en/user/
[13] “Geoserver Information”, Available: http://workshops.opengeo.org/
[14] Subham Roy, “Benchmarking on Spatial Database”, Internal Report IIT Bombay.