General talk about software patterns

[Joerg Simon <j_simon AT sbox.tugraz.at>]

Hello Pattern Experts! :)

[short: content:
- description of the problem
- notes
- whats I have to use
- what I tried/thought about
- End (Question)]

I am a novice in Patterns and wnated to ask for statements, help, new 
idears for my following Problem:

Actually I am making a Practical course at a facility at the Technical 
University Graz, where I am developing a Client for a tool they use 
internally.

At that client there should be a mapping from some Objects and too their 
Properties to a graphical representation in form of a graph. So for 
Instance it could be something like this:

Type A  ----> Node with Shape of a Circle

    A with Property a1 -> The border is fat
    A with Property a2, Value -> the Color varies between Green and 
Blue in 10 Steps according to the Value
    A with Property a3 -> NodeColor = green

Type B  ----> Node with Shape of a Triangle

    B with Property b1 -> The border is fat
    B with Property b2, value -> The color stroketype vaies according 
to the value

Type C -----> Link in form of a Polyline

    C with Property c1 -> End of Line is a small circle
    C with Property c2 -> End of line is a circle and an arrow

.....

Some things are to note: The Properties are all optional, I get Nodes 
and Links reported, however the Propertyies change for every Node/Link.

There might be that new Properties are added to the mapping after some 
time...

The mapping pf the Properies might change too (okay, it will ;), since 
it is a prototype and we first have to find the right mapping.... )

There should be a initial configuration which Property corespont to wich 
kind of mapping, the form of the configuration is not important at that 
point since it is a prototype, to this could be hardcodet in the 
programm, however it should be flexible.

Since this Prototype is a Windows Applikation we are coding in .NET {not 
my stuff normally ;) }, and for time-reasons the facility (the 
Know-Center at graz [www.know-center.at]) wants to bye the Nevron 
Diagram library (www.nevron.com), so the drawing of the diagramm works 
with that, and also the altering of shapes.

I have wrapperclasses for all the drawing done, since it fits easier in 
the model and we are shure we change the version of nevron as soon as 
the new one comes out, since this one desn't fit our needs.


What is defenite:

I have an Interface with which I get the elements reportet for drawing. 
There is a class which draws the nodes and makes the connection one by 
one. Since the mapping is always specific to just one element i also 
want to trigger the action at that drawing process.

I get the nodes reported in a very descriptive style, I get:
for Nodes:
the name of the node, used for labeling
an id, I use that to identify the node and make the connections
a dictionary with the properties. For those unfamiliar to .NET: a 
dictionary is a container with key/value pairs.
The Keys are the types of the Properties (like a1,a2,b1 in the example 
above) the values are optionally, but needed by some types.

What I thought about {and where i think it isn't good):

The maybe best idear at first:

IDEAR Nr. 1)

I am creating a function for every type of visual manipulation on the 
graph. I am having a hashtable where I store the Property as a key and a 
function pointer (a delegate in .NET i think) to the functions. There is 
an other function which is configuring that hashtable with the delegates.
Everytime I get a Object do draw I look in the Hashtable for the 
properties and call the registered functions.

Problems i see:
- There is no good way of extensibility according to the open-closed 
principle, which I want to follow here I think.
- I have to follow a specific set of parameters for every function if I 
don't want to have a big if then else if else part. If I get one the 
registration at a hashtable seems nonsence to me.
- I think too that it is hard to have different behavior for different 
reports which exist at the same time in the program (which might be 
true, but maybe not that important if we get a tooo complex solution for 
that problem {I am not shure if there is a simple one....})

IDEAR Nr.2

There are Objects for every type of visual manipulation of the graph. I 
am having some kind of store (like a hashtable) where I register the 
Objects to a property-key. So generally the same as above with objects:

Problems I see:
- The same with the decision code of fixed params as above
- There is the same problem with the different bahvior.

IDEAR Nr.3

Okay, now the things with too much patterns:

I thought of a chain of responibility, where I give the dictionary with 
the properties to appy inside as an argument, and every property who 
wants to have something to do with it makes it stuff. The Property class 
itself ist having an visual-mapping-object which is created over an 
abstract factory. There too exists a serier of visual mapping objects 
which implement the according behavior. The configuration is done by 
registering the right factories to the Properties Objects.

Problem I see:
- I tried do draw an UML diagram for that, and even here I got the 
feeling that is too complikated.

IDEAR Nr.4

Hm, I thought of making the visual mapping objects in means of a 
decorator pattern, who can be chained dogether. Everytime we have to 
draw an node/link the request is going to some desicion code (maybe too 
a chain of responibility), who just chains the decorators together so we 
get a configured element, on whom then a mapp() method is called

Problem I see:
- Okay, this was really much tooo much complcated and for our app 
defenitely an overkill.....

End (Question:)

Okay, none of the above solutions seemed satifacting to me, so I just 
wanted to ask for satements of my solution idears, and maybe idears what 
else I can do.
{okay, generally I am awaiting some magic pattern which is very easy to 
understand, very efficient, very fast, very small, easy to implement and 
so on ;) }

Thanks for any replies,
  Jörg Simon