Algorithms For Dummies

  Understanding Graph Basics 

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without really thinking about it. Of course, it helps to know that you won’t nor-

mally deal with the numbers behind the graphs. Think about a map. What you see 

is a graph, but you see it in graphic format, with cities, roads, and all sorts of other 

features. The thing is, when you see a map, you think about a map, not a graph 

(but your GPS does see a graph, which is why it can always suggest the shortest 

route to your destination). If you were to start looking around, you’d find many 

common items that are graphs but are called something else.

Some graphs aren’t visual in nature, but you still don’t see them as graphs. For 

example, telephone menu systems are a form of directional graph. In fact, for 

their seeming simplicity, telephone graphs are actually somewhat complex. They 

can include loops and all sorts of other interesting structures. Something you 

might try is to map out the graph for a menu system at some point. You might be 

surprised at just how complex some of them can be.

Another form of menu system appears as part of applications. To perform tasks, 

most applications take you through a series of steps in a special kind of 

subapplication  called  a  wizard.  The  use  of  wizards  make  seemingly  complex 

applications much easier to use, but to make the wizards work, the application 

developer must create a graph depicting the series of steps.

It may surprise you to find that even recipes in cookbooks are a kind of graph (and 

creating a pictorial representation of the relationships between ingredients can 

prove interesting). Each ingredient in the recipe is a node. The nodes connect 

using the edges created by the instructions for mixing the ingredients. Of course, 

a recipe is just a kind of chemistry, and chemical graphics show the relationship 

between elements in a molecule. (Yes, people actually are having this discussion; 

you can see one such thread at 

http://stackoverflow.com/questions/7749073/

representing-a-cooking-recipe-in-a-graph-database

.)

The point is that you see these graphs all the time, but you don’t see them as 

graphs — you see them as something else, such as a recipe or a chemical formula. 

Graphs can represent many kinds of relationships between objects, implying an 

order sequence, time dependence, or causality.