concept
directed acyclic graph
are referred to as an acyclic directed graph directed acyclic graph (directed acyclic graph), referred to as DAG FIG. Assuming that the data flow diagram indicating the construction plans of a project or program to the map, the map is not allowed in the loop, if the loop occurs, describes an activity in its own as a prerequisite, is clearly absurd, the project will not conduct.
Topological Sort
is a kind of topological sort linearizing nonlinear structure of the important means to FIG. In a given directed graph G, if the sequence of vertexes Vi1, Vi2, Vi3, ...., Vin ,. The following conditions: If the directed graph G from vertex Vi, Vj one path to the vertex, the vertex in the sequence must be before the vertex Vj Vi, then this sequence is called a topology sequence. Seeking a process referred to in FIG topology topological sorting sequence.
topological sorting method is as follows:
(1) selecting a penetration from the figure is O vertices and outputs;
(2) from FIG. Deletion of all the vertex and the vertex to the end of an arc the arc.
These two steps is repeated until all the vertices are output, the output sequence is the sequence of the non-cyclic topology of FIG.
if the belt right vertex represents the drawing event, showing the side with the activities there, the edge weights represent the cost of activity, there are known as the right side of this band to the active network of FIG. (activity on edge network), referred to as the AOE network. AOE network is a directed acyclic graph. AOE network is used to describe the method is complicated by a number of plans and projects consisting of cross-cutting activities, such as a project AOE network.
In the event represented by engineering side, the right side of this activity represents the time required to complete the vertices represent the beginning of an activity, known as the source vertex 1 point (or starting point), represents the entire commencement and 2 vertex called the sink (or end), indicating the end of the whole project. AOE network with the shortest estimated duration of the project (how much time is needed to complete the project at least), and which activities are key to affect the progress of the project.
Several terms
Path Length: The sum of the duration of each activity (i.e., ownership of the path and) on the path. Minimum time
to complete the project: from the project start point (source) to a completion point (sink) the shortest path is called the longest time to complete the project.
critical path: the path length of the longest path is called the critical path.
Nature
(1) only after a certain event occurs vertices represent, to get ready to have represented the starting side from the start vertex.
(2) only in the event each side to represent a point of entry have ended, when the event represented the apex take place.
critical path (critical path): AOE in the network from source to sink (end vertex) longest path. Activities on the critical path for critical activities.