Coverage And Relational Data Model

Question 1

How are data and tables constructed

Answer 1

Data consists if tables and relations. 
Rows define the cases objects, instances of some class of objects
The columns define the known properties or attributes

Question 2

what can go in the columns of a data models

Answer 2

Data (integers, floats, dates and text)
BLOBs (images, music, video)
Hyperlinks to wed pages
Links to initiate programs

Question 3

The relational data model

Answer 3

A county (entity) has a name, FILS pop90 and area are considered attributes
Data can be linked from different tables that are linked using unique IDs

Question 4

What is relational algebra

Answer 4

Relational algebra is the foundational underpinning of query languages for databases
It defines how relations (tables) can be manipulated and combines to form new relations
E.g projection reduced the number of attributes in a target table with respect to the source table

Question 5

What are feature classes

Answer 5

I. Arcgis feature classes are homogeneous collections of features with a common spatial representation and set of attributes stored in a database

Question 6

Give an example of a feature class

Answer 6

A line feature class for representing read centre lines

Question 7

Describe relationships between objects

Answer 7

Every arc points to two polygons
The outside world is s special polygons
Every arc ends in two nodes
Nodes have any number of arcs, sometimes limited to three
Polygons have any number of arcs, sometimes limited by design
Polygons must be closed

Question 8

Describe connectivity in arc node topology

Answer 8

This is a data structure starting from a Node, and ending at a node. Intersecting arcs are split

Question 9

Define area in topological concepts

Answer 9

Polygon arc topology is defined as an ordered list of arcs
Boundary model of polygons
Arc coordinates are not duplicated
Arclist is a list of arc creating polygon

Question 10

Describe contiguity in topology

Answer 10

This is defined to understand adjacency, e.g. left polygon and right polygon. This rests on the order of nodes

Question 11

What is a spatial data model

Answer 11

Defined as the objects in a spatial database plus the relationships amount them. It’s purpose is the provide a formal means of represent and manipulating spatially referenced information

Question 12

What is the purpose of coordinates

Answer 12

They are used to define the spatial location and extent of geographic objects

Question 13

What is the max values one/two bytes can store (of integer values)

Answer 13

256/65536

Question 14

What is ASCII code

Answer 14

ASCII code allows us to easily represent alphanumeric characters and numbers
Typically used for attribute information

Question 15

What is indicated in .shx files

Answer 15

Segments of roads are indexed by pointers , and the identifiers for connected segments

Question 16

What is the difference between a sub type and domain

Answer 16

Subtypes group based in class and a domain is the examples of possible forms of this class would be valid, restricting the value you can put in the domain