1. COMP 261 Lecture 2
Graphs 1 of 3

2. Outline Graph Learning objectives Assignments 1 and 2
Understand the data files
Read the files
Data structures for graphs

3. Graph Collection of nodes
Collection of edges (connections between nodes)
Many situations in the world
places/objects with connections
airports & flights, intersections & roads, network switches and cables ….
entities with relationships
social networks, biological models
web pages ….
states and actions
games, plans, …..

4. Graph Learning objectives Big block!
Produce a Google Maps-like program
Load & Display the map
Move / Zoom in and out
Store relevant information
Show matching list by name prefix
Highlight roads / places
Shortest path finding …
Big block!
~ 8 lectures
2 assignments

5. Graph Learning objectives
Design proper data structure to store graph (nodes, edges, …)
Display graph (zoom in/out, move, …)
Search the graph
pop-up matching street names while typing
shortest path finding
Understand the graph
Connected or disconnected?
Points that are critical for connectivity

6. Auckland Roads: Assignment 1
Load data into data structures
graph of intersections and roads
indexes for fast searching:
trie of road names
Display the map (and zoom in/out)
Select roads (by name)
Show all roads matching what is typed so far
Highlight road on map.
Select intersections (by mouse click)
Highlight intersection
Display names of roads at intersection.
Run the example program.

7. Auckland Roads: Assignment 2
Google maps / GPS navigation system:
Find shortest routes in graph between two intersections
Emergency planning
Identify disconnected parts of the road system
Identify all intersections that would disconnect part of the system.
All build on the graph structure of Assignment 1.

8. Assignment 1: step by step
Eclipse: “hello world” program
Technical notes: online eclipse tutorial
GUI.java is provided for you as abstract class
Example of its use is in SquaresExample.java
Your job is about representing the graph and drawing it similar to how squares are drawn!
Data files:
load data
each file can be a different object
draw: x, y
build/store the graph

9. SquaresExample Interface
Load data
Zoom in/out (+/-)
Move
Search street name
Display
Text field

10. Road Map program Main program
Needs field(s) to hold the road map data structures
Main method / constructor filling the field(s)
Learn to fulfil the GUI methods (redraw, onClick, onSearch, onMove, onLoad …) to make interesting things happen
Classes for RoadGraph, Roads, Intersections, Location…
Each class has the data structure and methods for loading/accessing/modifying

11. Program Summary Load the files Store the information into a graph
Roads: roadID-roadInfo.tab
Nodes: nodeID-lat-lon.tab
Road segments: roadSeg-roadID-length-nodeID-nodeID-coords.tab
Store the information into a graph
Data structure needed
Display (part of) the graph in the drawing area
Redraw the graph after movements (e.g. left, right, zoom in/out)

12. Loading Files
Roads (roadID-roadInfo.tab) roadid type name city 1way sp rc !car !ped !bic cowley st waterview walmer rd point chevalier carrington rd point chevalier Nodes (nodeID-lat-lon.tab) Road segments (roadSeg-roadID-length-nodeID-nodeID-coords.tab) roadID length nodeID1 nodeID2 coords
Read README.txt

13. Loading Files roads vs road segments
A road can have many intersections (e.g. Williamson Ave)
A road segment has no intersection in the middle
node = intersection
segments
nodes
road

14. Data Properties Road ID Type (no need to use) Name (match the search)
City
One-way or not (needed for shortest path finding)
Speed limit (needed for fastest path finding)
Road class (no need given speed limit)
notforcar, notforpede, notforbicy (special use, not needed for now)

15. Data Properties Node (No column title in file!) ID Latitude Longitude
Segment
RoadID (which road it belongs to)
Length (needed for shortest path finding)
NodeID1 (first node)
NodeID2 (second node)
Coords (for display, the segment might not be straight)
Direction of segment?
NodeID2
Coord4
Coord2
Coord3
Coord1
NodeID1

16. Reading data more efficiently
File
FileReader
BufferedReader
// Read file line by line
File roadFile = new File(dataDirectory+"roadID-roadInfo.tab");
BufferedReader data = new BufferedReader(new FileReader(roadFile));
String line = data.readLine();
// Process each line using split method
String[] values = line.split("\t");
int n = Integer.parseInt(values[0]);
double d = Double.parseDouble(values[1]);
Columns split by \t (tab)
Convert String to proper type!

17. Data Structures for Graphs
Straightforward design according to the columns in the file (each column is a field/variable in the class)
intersections = nodes, road segments = edges
Nodes
Edges A B C D E F G H 15 A C 3 A F 12 B D 18 D B 6 B H 71 C B ……

18. Data Structures for Graphs
A graph is typically represented as a set of nodes and a set of edges
Graph
Set<Node> nodes
Set<Edge> edges
Node
Information of a node: id, location, …
Edge
Information of an edge: id, two end-nodes, direction, …

19. Data Structures for Graphs
Different types of graphs
Multi-graph (multi-lane roads)
Directed edges (one-way streets)
Loops
Other complex properties
No turn right/left …
Represent an undirected edge as two directed edges? 22 C A 22 A C

20. More Data Structures for Graphs
What do we need to do with a graph?
Common actions on a graph
List all the nodes
List all the edges
Find all outgoing edges of a node
Find all incoming edges of a node
Find all the outgoing neighbours of a node
Find all the incoming neighbours of a node
Find out whether two nodes are connected or not
Find the edge between two nodes …
What do we need for the Road Map?
maybe same
if undirected