Glossary
The vocabulary of networks, in plain words.
- Network
- A set of nodes and the links between them. Mathematicians call it a graph.
- Node
- One of the things connected. Also called a vertex.
- Link
- A connection between two nodes. Also called an edge.
- Directed link
- A link with a direction, such as a hyperlink or a citation.
- Weighted link
- A link with a number attached: a distance, a capacity, a strength.
- Degree
- The number of links a node has.
- Degree distribution
- How many nodes have each possible degree. Its shape says whether the network has hubs.
- Path
- A sequence of links leading from one node to another.
- Shortest path
- The path between two nodes with the fewest links, or the lowest total weight.
- Diameter
- The longest of all the shortest paths in a network.
- Clustering coefficient
- The chance that two neighbours of a node are also linked to each other.
- Component
- A part of a network within which every node can reach every other.
- Giant component
- A single component containing a large share of all nodes.
- Hub
- A node with far more links than is typical.
- Centrality
- Any measure of how important a node is because of its position.
- Betweenness
- How often a node lies on the shortest paths between other nodes.
- Random graph
- A network whose links are placed by chance; the baseline that real networks are compared with.
- Small-world network
- A network that is highly clustered and yet has short paths between most pairs of nodes.
- Scale-free network
- A network whose degree distribution follows a power law, so that hubs of every size occur.
- Preferential attachment
- Growth in which new nodes are more likely to link to nodes that already have many links.
- Community
- A group of nodes linked more densely to one another than to the rest.
- Percolation
- The study of when a network stays connected as nodes or links are removed.
- Cascade
- A failure or a change that spreads from node to node.
- Network effect
- A service becoming more useful to each user as more people use it.
- Packet switching
- Sending data as small, separately routed blocks instead of over a reserved line.
- Protocol
- An agreed set of rules for exchanging messages.
- Layering
- Dividing communication into levels, each using only the service of the one below.
- End-to-end principle
- Put a function in the endpoints unless the network itself can do it completely and correctly.
- Routing
- Choosing the path that traffic takes through a network.
- Autonomous system
- One independently operated network within the internet.
- Peer-to-peer
- An arrangement in which participants connect directly as equals, with no central server.