Networks Flashcards
What does a network do?
Networks connect objects.
What questions does network information answer?
Network information answers a broad range of questions on connectivity, such as whether an object is reachable from another object, what is the shortest path is between them, how central an object is to a network, or how fast something will spread through the network and where it will spread to.
How are networks used
Network models are used in application domains of spatial information, ranging from navigation through hydrology to health: they allow for analysing spatial as well as non-spatial phenomena, such as social relations and the interactions between these.
What are objects ina network called?
Objects connected through a network are called nodes and the variety of objects that can play the role of nodes is unlimited and includes physical objects (such as people and cities) as well as mental and social ones (such as concepts and companies)
What connects pairs of nodes?
Pairs of nodes are connected by edges. They can be physical (such as roads) or conceptual (such as friendships). Every pair of nodes satisfying the relation is connected by an edge. Just like for nodes, a variety of relations can be used to define edges is also unlimited
What is the difference between directed and non-directed edges?
A road network that distinguishes driving directions is a directed network. two way connections in directed networks need to be represented by a separate edge for each direction. Some networks have multiple edges joining the same pair of nodes with the same direction, such as multiple lanes of highways.
What network application is considered a quantitative attribute?
A quantitative attribute of a network application is called a weight or impedance if the edge. For example, speed limits can serve as weights with higher speeds having greater weight or lower impedance.
What is a path in a network?
A path in a network is a sequence of nodes where each consecutive pair of nodes is connected by an edge (with an appropriate direction, if the edges are directed). Paths describe trajectories of something moving through a network. When there are multiple badges between any pair of nodes, paths need to be thought of as sequences of edges rather than nodes to remove ambiguity.
Lost some different terms describing directed networks
A node is said to be reachable from another node if there is a path connecting the two.
A path returning to its origin is a cycle.
A network is connected if it has a path between every pair of nodes.
What is an embedded network
A network can be embedded in a surface, or in another network, or in three dimensional space, giving its nodes positions in those spaces and shapes to edges.
How do networks form hierarchies?
Roads tend to be classified on the basis of their importance, producing road networks at multiple hierarchical levels, such as interstate, state and local roads
How are networks represented?
Networks are represented as graphs. In mathematicsX a graph is defined as a pair G = (N,E) comprising a set of nodes and edges. The edges are two-element sunsets of N, or ordered pairs in the case of directed networks.
What is the simplest encoding of a graph?
This simplistic coding is an adjacency matrix. It shows for every pair of nodes whether they are adjacent I.e. directly connected by an edge . The matrix rows and columns stand for the nodesC with elements (I,j) representing whether the nodes I and j are adjacent typically by binary values of 1 and 0. If edges are labelled, they get represented in an adjacency matrix by the values of the label attribute.
Give an example of a label I am adjacency matrix
A highway segment linking two cities may be labelled by its length, so that the adjacency matrix turned into a distance table for cities connected by highways, familiar from road atlases.
How is network data used?
The core computations for networks is the shortest path, the closest node, travelling salesman (the optimal location for trade).
