Transcript Attribute Data

Attribute Data
CampusID
Name
Type
Floors
6
Murphy
Academic
2
2001
9
Hopkins
Support
2
946
12
Maintenance
Support
1
1848
15
Hickey
Support
2
2367
17
Shay-Loughlen
Dorm
3
1298
CS 128/ES 228 - Lecture 6a
Footprint
1
Why Databases?

One of the advantages of vectorbased data is that each datum
corresponds to a (portion) of a “real”
object.

BUT… Objects are more than
geographic locations
CS 128/ES 228 - Lecture 6a
2
CampusID
Database
“Review”
Name
Type
Floors
Footprint
6
Murphy
Academic
2
2001
9
Hopkins
Support
2
946
12
Maintenance
Support
1
1848
15
Hickey
Support
2
2367
17
Shay-Loughlen
Dorm
3
1298
 Databases consist of tables
 Each table holds records
 Records are in rows
 Each record consists of fields, i.e.
individual data items
 Fields are in columns
 Fields that have unique values within a
table are called “keys”
CS 128/ES 228 - Lecture 6a
3
Sequential Databases
Once upon a time,
computer scientists tried to
put all the data for an
application in one table
It didn’t work
CS 128/ES 228 - Lecture 6a
4
Flaws of Sequential Databases

Not all data is homogeneous

Monolithic structure leads to
contention problems

Separation of data into “sub”
databases leads to duplication
(and inconsistencies)
CS 128/ES 228 - Lecture 6a
5
Relational databases

Use many (related) tables of data,
with minimal duplication

Tables are “linked” through common
values in particular fields

“Queries” permit rich “data mining”
CS 128/ES 228 - Lecture 6a
6
What Color Hair Does
Student 234 Have?
117
Mary
3.8
201
Dave
2.5
Mary
3.1 of a JOIN operation
This234
is anDawn
example
Dawn
235
Pete
3.2
382
Ted
2.6
378
Jane
3.0
444
Ann
4.0
Pete
Pat
CS 128/ES 228 - Lecture 6a
7
Relational Databases in GIS
One table traditionally holds
geographic information
 Other tables hold data about other
attributes
 Tables are linked through “Object
Ids”
 (Object Ids should be independent
of the software)

CS 128/ES 228 - Lecture 6a
8
Relational Databases in GIS

Consider a “Buildings” layer


“GIS” data includes location (including
coordinate system), symbology,
internal bookkeeping
“External” data includes name of
building, date built, purpose, etc.
CS 128/ES 228 - Lecture 6a
9
Sometimes they are mixed
CS 128/ES 228 - Lecture 6a
10
Queries

Information is
gained by
linking tables
through “joins”

Queries can
involve
computed
quantities, etc.
CS 128/ES 228 - Lecture 6a
11
Storing Topology

Shapefiles contain no topological
information

But topology is important
SOLUTION

Store the topology elsewhere
CS 128/ES 228 - Lecture 6a
12
Practicality
 GIS must maintain topology (to be
useful)
 GIS can’t store topology (in
shapefiles)
 SO, GIS must compute topology
CS 128/ES 228 - Lecture 6a
13
Data Structure for Topology
1
9
Zone Zone Bou
1
2
nd.
2
B
10
C
4
3
5
8
D
7
A
6
Select Boundary
Where Zone1=A
A
B
4
A
B
C
C
C
D
5
10
8
Ans: 4,5
CS 128/ES 228 - Lecture 6a
14
Topological Operations

Split one region into two
B
A
C
Name
Color
Area
A
Green
275
Name
Color
Area
B
Green
190
C
Green
85
CS 128/ES 228 - Lecture 6a
15
Topological Operations

Merge two regions into one
A
C
B
Name
Color
Area
A
Green
190
B
Red
85
Name
Color
Area
C
???
275
CS 128/ES 228 - Lecture 6a
16
Dealing with topological operations
Union (whose data
dominates if there is a
conflict?)
 Intersect (whose data do
we keep?)
 “Snaps”
 Clipping (cropping) a raster
OR a vector

CS 128/ES 228 - Lecture 6a
17
Issues with large GIS’s

Currency

How do keep the data up to date?
CS 128/ES 228 - Lecture 6a
18
Where does currency arise
in GIS’s?

Many Places
Real-time weather (or other
environmental) data
 Tracking vehicles
 Tracking prisoners – be careful where
you put the tracking collar!
 …

CS 128/ES 228 - Lecture 6a
19
Issues with large GIS’s

Concurrency

How do we prevent conflicts?

One way is to permit “read only”
• Works for systems like FRIAR
• Does not work when “transactions” must be
made
CS 128/ES 228 - Lecture 6a
20
A Concurrency Skit
Scene: One seat (8B) is left on
Friday’s flight to Cancun.
 Time 1: Ted calls up travel agent
and asks if any seats are left. Is
told yes.
 Time 2: Dave calls up different
travel agent and asks if any seats
are left. Is told yes.

CS 128/ES 228 - Lecture 6a
21
A Concurrency Skit
(continued)
Time 3: Ted’s agent books his seat.
 Time 4: Dave’s agent books his
seat.
 Scene 2: Friday afternoon at the
airport...
(action to be ad-libbed)

CS 128/ES 228 - Lecture 6a
22
Where does concurrency
arise in GIS’s?

The are not that common, but some
examples include:
Issuing orders to vehicles in the field.
 Updating claims on gold mines

CS 128/ES 228 - Lecture 6a
23
Issues with large GIS’s

Security


Of proprietary data
Legal/ethical concerns
Massachusetts mileage tax
 Rental car tracking
 Traffic reports (what if they’re wrong?)

CS 128/ES 228 - Lecture 6a
24
What distinguishes (some) GIS’s

The types of these operations that
they can perform.
Both Database and Topological
CS 128/ES 228 - Lecture 6a
25