afnix-gfx






gfx ‐ standard graph module

The Standard Graphmodule is an original implementation
dedicated to the graph moddeling and manipulation. At the
heart of this module is the concept of edges and vertices.

     Graphconcepts
The afnix‐gfxmodule provides the support for manipulating
graphs. Formally a graph is a collection of edges and
vertices. In a normal graph, an edge connects two vertices.
On the other hand, a vertex can have several edges. When an
edge connects several vertices, it is called an hyperedge
and the resulting structure is called an hypergraph.

     Edgeclass
The Edgeclass is a class used for a graph construction in
association with the Vertexclass. An edge is used to connect
vertices. Normally, an edge connects two vertices. The
number of vertices attached to an edge is called the
cardinality of that edge. When the edge cardinality is one,
the edge is called a self‐loop. This mean that the edge
connects the vertex to itself. This last point is merely a
definition but present the advantage of defining an
hyperedge as a set of vertices.

     Vertexclass
The Vertexis the other class used for the graph
construction. and operates with the edgeclass. A vertex is
used to reference edges. the number of edges referenced by a
vertex is called the degree of that vertex.

     Graph
The Graphclass is class that represent either a graph or a
hypergraph. By definition, a graph is collection of edges
and vertices. There are numerous property attached to graph.
Formally, a graph consists of a set of edges, a set of
vertices and the associated endpoints. However, the
implementation is designed in a way so that each edge and
vertex carry its associated objects. This method ensures
that the graph is fully defined by only its two sets.

     Graphconstruction
The graph construction is quite simple and proceed by adding
edges and vertices. The base system does not enforce rules
on the graph structure. it is possible to add con connected
vertices as well as unreferenced edges.

     Edgeconstruction
An edge is constructed by simply invoking the default
constructor. Optionally, a client object can be attached to
the edge.

# create a default edge
const edge (afnix:gfx:Edge)









                             ‐2‐


# create an edge with a client object
const hello (afnix:gfx:Edge "hello")

The edge‐ppredicate can be used to check for the object
type. When an edge is created with client object, the get‐
clientmethod can be used to access that object.

     Vertexconstruction
A vertex is constructed a way similar to the Edge>object.
The vertex is constructed by simply invoking the default
constructor. Optionally, a client object can be attached to
the edge.

# create a default vertex
const vrtx (afnix:gfx:Vertex)
# create an vertex with a client object
const world (afnix:gfx:Vertex "world")

The vertex‐ppredicate can be used to check for the object
type. When a vertex is created with a client object, the
get‐clientmethod can be used to access that object.

     Graphconstruction
A graph is constructed by simply adding edges and vertices
to it. The graph‐ppredicate can be use to assert the graph
type. the graph class also supports the concept of client
object which can be attached at construction or with the
set‐clientmethod.

const graph (afnix:gfx:Graph)

The addmethod can be used to add edges or vertices to the
graph. The important point is that during the construction
process, the graph structure is updated with the proper
number of edge and vertices.

# create a graph
const  g    (afnix:gfx:Graph)
assert true (afnix:gfx:graph‐p g)
# create an edge and add vertices
const edge (afnix:gfx:Edge)
edge:add   (afnix:gfx:Vertex "hello")
edge:add   (afnix:gfx:Vertex "world")
assert 2   (edge:degree)
# add the edge to the graph and check
g:add edge
assert 1 (g:number‐of‐edges)
assert 2 (g:number‐of‐vertices)
# check for nodes and edges
assert true (afnix:gfx:edge‐p   (g:get‐edge   0))
assert true (afnix:gfx:vertex‐p (g:get‐vertex 0))
assert true (afnix:gfx:vertex‐p (g:get‐vertex 1))











                             ‐3‐




     Edge
The Edgeclass is a class used for a graph construction in
association with the Vertexclass. An edge is used to connect
vertices. Normally, an edge connects two vertices. The
number of vertices attached to an edge is called the
cardinality of that edge. A client object can also be
attached to the class.

     Predicate

     edge‐p

     Inheritance

     Object

     Constructors

     Edge(none)
     The Edgeconstructor create an empty edge.

     Edge(Object)
     The Edgeconstructor create an edge with a client
     object.

     Methods

     nonereset‐>
     The resetmethod reset all vertices attached to the
     edge.

     Integercardinality‐>
     The cardinalitymethod returns the cardinality of the
     edge. The cardinality of an edge is the number of
     attached vertices.

     Vertexadd‐>
     The addmethod attach a vertex to this edge. The method
     return the argument vertex.

     Vertexget‐>
     The getmethod returns the attached vertex by index. If
     the index is out‐of range, and exception is raised.

     Objectget‐client‐>
     The get‐clientmethod returns the edge client object. If
     the client object is not set, nil is returned.

     Objectset‐client‐>
     The set‐clientmethod sets the edge client object. The
     object is returned by this method.










                             ‐4‐


     Vertex
The Vertexclass is a class used for a graph construction in
association with the Edgeclass. An vertex is an edge node.
The number of edges referenced by a vertex is called the
degree of that vertex. A client object can also be attached
to the object.

     Predicate

     vertex‐p

     Inheritance

     Object

     Constructors

     Vertex(none)
     The Vertexconstructor create an empty vertex.

     Vertex(Object)
     The Vertexconstructor create a vertex with a client
     object.

     Methods

     nonereset‐>
     The resetmethod reset all edges attached to the vertex.

     Integerdegree‐>
     The degreemethod returns the degree of the vertex. The
     degree of a vertex is the number of referenced edges.

     Edgeadd‐>
     The addmethod references an edge with this vertex. The
     method return the argument edge.

     Edgeget‐>
     The getmethod returns the referenced edge by index. If
     the index is out‐of range, and exception is raised.

     Objectget‐client‐>
     The get‐clientmethod returns the vertex client object.
     If the client object is not set, nil is returned.

     Objectset‐client‐>
     The set‐clientmethod sets the vertex client object. The
     object is returned by this method.

     Graph
The Graphobject is a general graph class that manages a set
of edges and vertices. The graph operates by adding edges
and vertices to it. The graph object also accepts a client
object in a way similar to the Edgeand Vertexclasses









                             ‐5‐


     Predicate

     graph‐p

     Inheritance

     Object

     Constructors

     Graph(none)
     The Graphconstructor create an empty graph.

     Graph(Object)
     The Graphconstructor create a graph with a client
     object.

     Methods

     nonereset‐>
     The resetmethod reset the graph

     nonereset‐edges‐>
     The reset‐edgesmethod reset all edges attached to the
     graph.

     nonereset‐vertices‐>
     The reset‐verticesmethod reset all vertices attached to
     the graph.

     Objectadd‐>
     The addmethod adds a vertex or an edge to the graph.
     When adding an edge, the methods check that the source
     and target vertices are also part of the graph.

     Booleanexists‐>
     The existsmethod returns true if the vertex or edge
     argument exists in the graph.

     Edgeget‐edge‐>
     The get‐edgemethod returns an edge by index. If the
     index is out‐of‐range, an exception is raised.

     Vertexget‐vertex‐>
     The get‐vertexmethod returns a vertex by index. If the
     index is out‐of‐range, an exception is raised.

     Integernumber‐of‐vertices‐>
     The number‐of‐verticesmethods returns the number of
     vertices in the graph.

     Integernumber‐of‐edges‐>
     The number‐of‐edgesmethods returns the number of edges
     in the graph.









                             ‐6‐


     Objectget‐client‐>
     The get‐clientmethod returns the graph client object.
     If the client object is not set, nil is returned.

     Objectset‐client‐>
     The set‐clientmethod sets the graph client object. The
     object is returned by this method.