2013 Topic 8 Database Design II - Schemas

8/13/2019 2013 Topic 8 Database Design II - Schemas

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DESIGNING THE DATABASE

(ii)

The implementation model:

Managing the attributes

(a forestry example)


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References:

GIS A Computing Perspective, M.F.

Worboys (with M.J. Duckham for

second edition). Taylor &Francis,

London, 2004. Ch. 2.


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Why are we concerned with the

database design?

Database design mostly concerns the attributes of

the real world objects represented in the GIS.

In modern GIS packages changing the attributes

is rather easyas in adding extra columns tothe attribute tables and putting in values.

But care should be taken to avoid putting the

same attributes into several tables as this maythreaten the integrity of the database (e.g.

Landparcel/landcover/house). We maintain

integrity through the DML task of JOIN.....


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What does a JOIN need?

ANS:

Appropriate PRIMARY keys

COMMON keysFOREIGN keys

The processes we look at today will helpensure these are correctly allocated,

inserted and used, based on different

IMPLEMENTATION MODELS


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The depth of a workers involvement in

GIS influences the Implementation Model

used

the external model(for those who use theGIS generated information);

the conceptual model(for those whogenerate the GIS information);

the internalmodel (for those who design

and construct the GIS database whichgenerates the GIS information); and

the phys ical model (for those wi threspons ibi l i ty for how the data are actually

sto red on the sto rage devices).


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Resulting in:

EXTERNAL SCHEMA

CONCEPTUAL SCHEMA INTERNAL (or LOGICAL) SCHEMA

(physical schema)

note: Schema = Graphic Diagrams


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The External schema is that understood by theprofessional for whom the DBM System (DBMS)offers decision support in the task of administrating,

for example, schools or health centres. Theprofessional may never actually be able, or required,to build or manipulate the DBMS (which isincorporated in the GIS).

At this external level there will be different perceptions thus different external implementation modelsexisting for different perceptions.

For example, certain real world entities such asphysician/forest may, by some, be seen to beentities in their own right, but by others merely as anattribute (e.g. of a clinic/landparcel).


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Preparation for design at theexternal level (to produce the

external schema of theimplementation model)

Identify stakeholders (main and subsidiary)

Examine working practices/rules of the

(main and subsidiary) stakeholders

Establish spatial rules (GIS not other IS)


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An external view by a health

administrator concerned with

facilities


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another external view

perhaps that of an administrator

concerned with HR


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external view by an education

administrator


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alternate external view


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considering working rules

Health andSafety Executive


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considering working rules

Local PoliceStation


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The conceptual level of the implementation modelis that understood by the DBMS operator or user,who will know (or will be able to know) which entities

are reallyrepresented in the database and whattheir attributes are. The DBMS operator will eitherknowor via a data dictionarybe able to find outhow data on entities and attributes are stored in the

database.

For example from the data dictionary the operator willbe able to find out what Foreign Keys an entity

holds; or that the attribute YOC represents Year-of-Construction; or whether an attribute is representedas a character variable, numerical variable (oranother type) and how it should be expressed, etc.


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Two steps to generate

CONCEPTUAL SCHEMA

1. Form the network schema

2. Form the ERM (Entity-

Relation Model) model


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Network schema (1)


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Network Schema (2)


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ERM

of Sports or

Educat ion


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West District East District

South District

NATION

District

Forest

Tree Firepath

1

m

m

n

1

m m


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f


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Finally from the conceptual

schema, produce a preliminary list

of entities and their attributesFOREST area, perimeter, owner, main-tree-

species..+UID, FK1, FK2

TREE species, YOP, forest..+UID, FK1, FK2DISTRICT name, area, perimeter, capital, chief-

executive.+UID, FK1, FK2

FIREPATH width, length, slope..+UID, FK1, FK2

SCHOOL name, address, director, no-of-students..+UID, FK1, FK2

Primary key

Foreign Key


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The Internal (or Logical) level is usually

that understood by the Database (DB)

Designer (sometimes called the GIS

Designer in the context of GIS) and theDatabase Administrator (DBA).


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Every identified ENTITY is listed with its attributes one of theseattributes being its unique identifier (underlined, below):

MINISTER (Ministers_NI_Nr, MINISTRY_NAME, MINISTRY_Code_NRSALARY_BAND.)

DIRECTOR (Directors_NI_Nr, DIRECTORATE, SALARY BAND.)

SCHOOL (SCHOOL_NR, Heads_NI_Nr,DIRECTORs_NI_Nr,ADDRESS, ...)

FOREST (FOREST_NR, Forest_NAME, YOP, AREA, PERIMETER..)

FIREPATH (FIREPATH_NR, FOREST_NR,YOC, LENGTH, WIDTH.)

TREE (TREE_NR, FOREST_NR,YOP, SPECIES, HEIGHT.)


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Then the dependent entitiesespecially if the

relationship is mandatorymust have a Foreign

Key (bold red below) added:

DIRECTOR(DIRECTORs_NI_NR, Directorate,

Ministry_Code_Nr, NAME, DOB,

HOME_ADDRESS) SCHOOL (SCHOOL_NR, DIRECTORS_NI_NR,

HEAD, SCHOOL_ADDRESS, SCHOOL TYPE)

FIREPATH (FIREPATH_NR, FOREST_NR, YOC,LENGTH, WIDTH, SLOPE)

TREE(TREE_NR, FOREST_NR, YOP,

MAJORITY_SPECIES, VALUE_1990)


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sometimes shown graphically

Note: if the conceptual schema was well made, then establishing the logicalschema is easy..


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A further example..


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The case study

Commercial timber companies wish, together, todesign and implement a GIS to increaseefficiencies.

The Ministry of Forestry will provide some support,and possibly the Ministry of Tourism and touroperators as they all need some informationrelated to forests, for their own decision support.

How can a GIS be designed to meet the needs ofthese (financial) supporters?


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Spatial RULES - 1


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Spatial RULES -2

1. A commercial forest is completely covered by

contiguous polygons of forest stands or clearings.2. The forest can be crossed by linear features such as

roads, paths, etc., which results in the subdivision ofthe stands and clearings into sub-stands or sub-clearingsboth can be referred to as forestry

management units.3. Plant or animal habitats are non-contiguous polygons

which overlie one or more forest stand or clearingpolygons, and may extend beyond one commercialforest into another, or into non commercial forest land.

4. Within the forest are human sites (e.g. restaurants,toilets, storage sheds, points of interest) andwatchtowers represented as point features, which mayor may not be accessible by paths, tracks, etc.


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External schemacommercial

timber company

Year of clearing

No. of carriageways

Year of Planting

Road,Track,PathSegments


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External schemaMin. Forestry


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External schemaMin. of Tourism


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External Schematour operators

Forest walking

Tour

Road, Track, Pathsegments

Forest Stand/ Clearing L,R

Nearby Watch Tower

1,2,3


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CONCEPTUAL SCHEMA -1


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CONCEPTUAL SCHEMA - 2

1

m

m

1

1

1

m

m

m

m

m


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Internal schema

Relation Attributes

TIMBER_COMPANY TC_UID, NAME, CONTACT, CEO, MINISTRY_NR

FOREST F_UID, TC_UID, NAME, ACREAGE, LA

STAND_or_CLEARING SC_UID, F_UID, FOREST_SPECIES_1,

FOREST_SPECIES_2

HABITAT H_UID, F_UID1, F_UID2, SPECIES_1, SPECIES_2ROAD_TRACK_or_PATH RTP_UID, T_UID, F_UID, FMU_UID_1, FMU_UID_2,

WIDTH, SURFACE, YOC, NR_TRACKS

FORESTRY_MANAGEMENT_UNIT FMU_UID, SC_UID, ACREAGE

HUMAN_SITE HS_UID, FMU_UID, RTP_UID, NAME, CONTACT,

CEO, RESOURCE

TOUR_OPERATOR TO_UID, NAME, CONTACT, CEO, MINISTRY_CONTACT

TOUR T_UID, TO_UID, COST, START, END, WAYPOINT1,WAYPOINT2, WAYPOINT3, WAYPOINT4

WATCH_TOWER WT_UID, SC_UID, HEIGHT, CONTACT, CEO


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DATA DICTIONARY

This contains instructions for the system operators to follow as they define (build) thedatabase. Some entries might be:

Relation: TIMBER_COMPANY

TC_UID width 11, integer, unique identifier of Timber Company

provided by the DBA

NAME width 20, character, legal name of the company

CONTACT width 14, character, telephone number of registered office

CEO width 20, character, firstname_middleinitial_familyname ofchief executive officer of timber company

MINISTRY_NR width 11, integer, unique identifier of Ministry provided bythe DBA

Relation: FOREST

F_UID width 11, integer, unique identifier of Forest provided bythe DBA

TC_UID width 11, numeric, unique identifier of Timber Companyprovided by the DBA

NAME width 20, character, name of the forest

ACREAGE width 14, numeric, areal dimension of forest in hectares

LA width 20, character, name of the Local Authority


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..small fragments of relations

NR


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do th is

Start the relation (table) for two more relations (as

has already been done for TIMBER_COMPANYand FOREST), and, using Excel, populate these

new relations for at least two entities..for

example STAND_OR_CLEARING or

WATCHTOWER .. using fictional (or real orimagined or simulated) data.

for subm ission (by 17:00 1s tNovember 2013)

and summative assessment (5%)..

Thank you!


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RELATIONS:STAND_OR_CLEARING

WATCHTOWER


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2013 Topic 8 Database Design II - Schemas

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