# cdt glossary [Graph]

Date: Fri, 11 Jan 2008 21:22:59 +0100

Message-ID: <4787cf03$0$85796$e4fe514c_at_news.xs4all.nl>

David BL wrote:

> mAsterdam wrote:

>> David BL wrote: >>> Keith H Duggar wrote: >>>> David BL wrote: >>>>> Marshall wrote: >>>>>> An interesting note, by the way: functions are relations... >>>>> Isn't it more precise to say that the graph of a function is a >>>>> relation? >>>> No, it isn't. >>>> http://mathworld.wolfram.com/Function.html >>> From mathworld a relation >>> http://mathworld.wolfram.com/Relation.html >>> is defined as a subset of a cartesian product. If a function is a >>> relation why do they define a graph of a function f as >>> { (x,f(x)) | x in domain of f }, >>> as described in >>> http://mathworld.wolfram.com/FunctionGraph.html >> That is 'graph' meaning 'plot', not 'a collection of vertices and >> edges'. In cdt it is the latter meaning that is mostly used (when >> discussing network and hierarchical databases).

*>*

> Yes, overloading "graph" can cause confusion.

*>*

[snip competing, possibly confusing definitions of 'function']

> Saying that a function is a relation of course makes a lot of sense.

*> However there can be some confusion. For example, the co-domain of a*

*> function can be referred to as one of the domains!*

One could construct misinterprations here, but I haven't seen them. The glossary's goal is not to anticipate and eliminate all thinkable confusions by re-creating language (read the preamble).

http://groups.google.com/group/comp.databases.theory/browse_thread/thread/49d94f43265f0921

Just helping to avoid boring repetitons of real cdt miscommunications with a list of suspect words turned out more ambitious than I thought. Try some ToDo's (they are at the end of the glossary): you'll be surprised of how much effort it will take.

Here is my proposal. Please do not (just) comment, but provide your improved text, so I can copy and paste it into the next glossary edition.

[Graph] (proposed text)

Most regulars at cdt use "graph" unqualified to mean
"a collection of vertices and edges",

not in the sense of "plot", "chart" or "diagram".

Both meanings have nice articles at Wikipedia. If you intend to use it in the second meaning, qualify it, or better yet: don't - just say plot, chart, or diagram. You have been warned :-)

-- What you see depends on where you stand.Received on Fri Jan 11 2008 - 21:22:59 CET