Spatial SQL: A Query and Presentation Language

Max J. Egenhofer

(Presenter: Yi-Shin Chen)

Outline

Introduction Spatial query language

Guidelines for an SQL Extension Requirements for Spatial Query Languages

Separating retrieval and display instructions Spatial SQL

Spatial domain, operations, data definition, selecting by pointing

GPL Display Mode, variables, scale, window, context, content

Conclusion

Introduction

The need for spatial query language Geographic Information System (GIS), Image Database,

Remote Sensing

Existing query languages are insufficient Only address the particular properties of lexical data

Treat spatial data as integers and strings

Spatial Data have additional properties Geometry

Graphical presentation

Example

SELECT ImageNameFROM S_ImagesWHERE RECTANGLE(-77.748125, 38.695 , -77.348125 , 39.095) OVERLAPS area

image4/W775647N389000.jpgimage4/W775644N388927.jpgimage4/W775644N388855.jpgimage4/W775641N388783.jpgimage4/W775555N389000.jpgimage4/W775552N388927.jpgimage4/W775550N388855.jpgimage4/W775547N388783.jpgimage4/W775463N389002.jpgimage4/W775461N388930.jpgimage4/W775458N388858.jpgimage4/W775455N388786.jpg

Query Result :

Introduction -II

Extending an existing language with spatial concepts

Reason: spatial databases contain both spatial and non-spatial data that will be the subject of user queries

SQL + Spatial Concepts = Spatial SQL

Guidelines for an SQL Extension

SELECT-FROM-WHERE clause should keep Three categories of queries

Exclusively about spatial properties About non-spatial properties Combine spatial and non-spatial properties

Should allow the user to pose non-spatial queries appropriately

SELECT-FROM-WHERE is already complex enough to use

Requirements for Spatial Query Languages

GEOQL Extended SQL

PSQL KGIS TIGRIS

Spatial ADT + + + + +

Graphical Presentation + + + + +

Result Combination +

Display of context + +

Content Examination

Selection by Pointing + +

Display manipulation +

Legend

Labels +

Selection of Map Scale +

Area of Interest +

Separating Retrieval and Display Instructions

User expectations Pose several queries in a raw Only modify the graphical parameter of objects

Integration of a full display description into the query language would make each user query unnecessarily complex and long

Retrieval language -> Spatial SQL Presentation language -> GPL

Spatial Domain

Provides a higher level abstraction of data

Four spatial domains: Spatial_0, Spatial_1, Spatial_2, Spatial_3

Spatial relationships refer to spatial concepts

such as topology and metric

Only the specified spatial operations and

relationships apply to spatial attributes

Spatial Data Definition

In general, a spatial relation will have exactly one spatial attributeCREATE TABLE city

(name char(100)

geometry spatial_2);

Spatial SQL does not prevent from defining several spatial attributes for a objectCREATE TABLE ocean

(name char(100)

geometry spatial_2

generalized_geometry spatial_0);

Spatial Operations – part one

Functions upon a spatial attribute Dimension, boundary, interior, bounding-Nodes,

bounding-Edges, interior-Nodes, interior-AreasSELECT boundary (geometry)

FROM city

WHERE name = “Los Angeles”

Deal with arithmetic operations Length, area, volume, perimeter, extreme coordinates,

complement, convex hullSELECT area (geometry)

FROM city

WHERE name = “Los Angeles”

Spatial Operations – part two

Binary spatial operations Distance, direction, angle, minimum, average Prefix formulation [Distance(city.geometry, highway.geometry)]

SELECT city.name FROM city, oceanWHERE distance (city.geometry, ocean.geometry) < 100KM

Binary topologies relationships Disjoint, meet, overlap, covers, inside, contains, equal,

left/right, north/south, over/underSELECT city.name FROM city, oceanWHERE city.geometry MEET ocean.geometry

Selection by Pointing

Interactive communication with drawing is enabled with the PICK qualifier which allows users to formulate queries.

SELECT name

FROM city

WHERE geometry=PICK

Ambiguities in the selection may exist User will be offered the possible choices and then

asked to identify the target

GPL

The concept of the display environment The query result is rendered according the

display description Offers instructions to SET or CANCEL a

graphic specification (can be qualified with PERMANENT)SET MODE highlight

With IMMEDIATELY to update the current display prior to asking the next querySET IMMEDIATELY COLOR red

Display Mode

Six display mode Conventional alphanumeric display NEW: starting a new drawing ex. SET MODE new; OVERLAY: adding the result onto a existing drawing REMOVE: erasing the result from a drawing INTERSECT: determining the common objects on the

display and in the query result HIGHLIGHT: emphasizing the result

Non-spatial attributes in the SELECT clause will be represented as label

Visual Variables

Graphic attributes can be specified for either an entire spatial relation or instances of spatial relationsSET LEGEND

COLOR black

PATTERN dashed User can check the current setting by “looking

at the legend” This part of GPL depends upon the user’s

hardware

Scale and Window

The scale of the graphical presentation can be described with the command SET SCALESET SCALE n (representing a scale factor of 1:n)

The window describing the area to be displayed can be described with SET WINDOW

The window can be determined by two pairs of coordinates the minimal bounding rectangle from the result

SET WINDOWSELECT geometryFROM roadWHERE town.name = “Orono”;

Context

The interpretation of graphical presentation is extremely depend on the context and environment

GPL allows the user to define spatial relation with SET CONTEXT as graphical context which is during query processing merged with the actual user query

SET CONTEXTFOR road.geometry

SELECT building.geometry, road.name

FROM road.parcel, building;

Content

A needed control mechanism with which user

may examine the content of a drawing

The content is the logical combination of

queries the result of which were combined

with OVERLAY and REMOVE

Content is only observable (cannot SET or

MODIFY)

SHOW Content

Conclusion

Spatial SQL +GPL

Spatial ADT +

Graphical Presentation +

Result Combination +

Display of context +

Content Examination +

Selection by Pointing +

Display manipulation +

Legend +

Labels +

Selection of Map Scale +

Area of Interest +

Appendix

Conventional Spatial Database Geodetic DataBlade Module

http://examples.informix.com/frameset.html#top?initial_page=/doc/case_studies/datablade/geo/geoLOC.html

NCR Teradata Object Relational Database (TOR) Oracle Spatial ESRI Spatial Database Engine (SDE)

systems like Oracle, Microsoft SQL Server, Sybase, IBM DB2, and Informix