Some relational operators

• intersection– result are all those tuples that are present in

both of the “input” relationsMarried couplesBob MaryJim DebbieJanice Tom

Fayetteville ResidentsJim DebbieFrank JoanFred Elaine

IntersectionJim Debbie

UnionMarried couplesBob MaryJim DebbieJanice Tom

Fayetteville ResidentsJim DebbieFrank JoanFred Elaine

UNIONBob MaryJim DebbieJanice TomFrank JoanFred Elaine

DifferenceMarried couplesBob MaryJim DebbieJanice Tom

Fayetteville ResidentsJim DebbieFrank JoanFred Elaine

DIFFERENCEBob MaryJanice Tom

Join

• parcel, owner• PARCEL(Parcel_ID, SIZE, Use, ETC…, Owner-ID)• OWNER(Owner-ID, Last_name, First_name, Street,

Town, ZIP)• JOIN• 123 240 acres, agricultural, Jones, Bob, Main,

Weddington, 23456• 567 1 acre, residential, Smith, Bill, College,

Fayetteville, 72701

Cartesian product• Important term “Cartesian product”

– results when two (or more) relations are “joined”

– see example on page 481– important concept because can be the

unexpected result of a join operation

Suppose we have our parcel data base

• owner table, parcel table etc.

• we wish to have list of all owned parcels

• suppose we have 4 owners and 6 parcels

• we could have a Cartesian product that had 24 “parcel owner” tuples even though there are only six parcels

Relational Projection

• selection of particular single attribute (COLUMNS) from a relation

• OWNER(Owner-ID, Last_name, First_name, Street, Town, ZIP)

• PROJECT Last_name– Smith

– Jones

– Brown

Restriction aka selection

• selection of particular tuples (ROWS) based on a criteria or condition– parcels larger than 200 acres

• the condition is called a predicate

Division

• given two tables • Desired_Land_USE(land-use) - where land use is

agriculture and timber• PARCEL(Parcel_ID, SIZE, Use, ETC…, Owner-

ID)• DIVISION

– result those parcels where Use is either agriculture or timber

Different operations

• can be grouped by – whether they operate on tuples or attributes

• all ate tuples except for projection

– how many relations they involve• single relation

– conditional selection

– restriction

– projection

• multiple relations (2..N)– joins

• binary - two relations– all others

Normalization• can be viewed essentially as the reduction of repetition in relations

– ex:• Not normalized

– PARCELS(Parcel-ID, Owner, Size,….» 123 SMITH 200» 123 JONES 200» 123 BROWN» 345 WATER» 555 WHITE

• Normalize– PARCEL(Parcel-ID, Size, Etc, ….– OWNER(Last_name, First_Name, Parcel-ID, etc…)

• Fully Normalized– PARCEL(Parcel-ID, Size, etc….)– OWNERSHIP(Parcel-ID, Owner-ID)– OWNERS(Owner-ID, Last_name, First_name, …..)

For spatial data

• Non-normalized spatial data– POLYGON(Polygon-ID,Segment-ID)

– COORD(Segment_ID,Start-X, Start-Y, End-X, End-Y)

– Example– Segment Start-X, Start-Y, End-X, End-Y

– 1 2 2 3 5

– 2 3 5 4 2

– 3 4 2 2 2

• What if we want to edit file and change location of one vertex?

• We must be sure to edit two records

Normalized spatial data– POLYGON(Polygon-ID,Segment-ID)– SEGMENT(Segment-ID, Start-point-ID, End-point-ID)– COORDS(Point-ID, X, Y)– SEGMENTS

• Segment-ID Start-point-ID End-point-ID

• 1 11 12

• 2 12 13

• 3 13 11

– COORDS• Point-ID X Y

• 11 2 2

• 12 3 5

• 13 4 2

Structured query language in geomatics

• SELECT <attribute list>

• FROM <table list>

• WHERE <condition>

Parcel Database Structure

Obtain addresses of neighbors of Anne

The SQL statement

Perimeter of Ann’s parcel• SELECT A.Parcel-ID• SUM(SQR ((D.X -E.X) * (D.X - E.X) + (D.Y - E.Y) * (D.Y -

E.Y)))• FROM OWNERS-PARCEL A, PARCEL-SEGMENT B,

SEGMENT-ENDPOINTS C, COORDINATES D, COORDINATES E

• WHERE A.Owner_name = ‘Ann”• AND A.Parcel-ID = B.Parcel-ID• AND B.Segment-ID = C.Segment-ID• AND C.Point1-ID = D.Point-ID• AND C.Point2-ID = E.Point-ID

Address of Parcel 345• SELECT Street-ID

• FROM PARCEL_SEGMENT, STREET-SEGMENT

• WHERE Parcel-ID = 345

• AND PARCEL-SEGMENT.Segment-ID = STREET-SEGMENT.Segment-ID

• SELECT Street-Name

• FROM PARCEL_SEGMENT, STREET-SEGMENT, STREET

• WHERE Parcel-ID = 345

• AND PARCEL-SEGMENT.Segment-ID = STREET-SEGMENT.Segment-ID

• AND STREET-SEGMENT.Street-ID = STREET.Street-ID