Unified Modeling Language (UML)

UML

Figure 1 shows an example of a class diagram.

Note the different type of arrows connecting the nodes.

Figure 1: Example of a UML class diagram generated with yEd.

Figure 2: Example of a UML class diagram generated with PlantUML.

Graphs are saved as graphml files (an XML format), but you can also export them as PNG or SVG.
ctrl f to search a graph, you can also dock the search window. Then use the Nodes tab to select based on label text (or however else you want to search it).
Alt + Shift + g to use an organic layout of the graph.
Alt + Shift + h to use the heirarchical layout of the graph.
In the property of a UML node there are textboxes that allow you to enter methods and attributes

Figure 3: Example of a visualisation of a database schema generated with yEd.

There is a spacemacs layer for PlantUML.
The file extension is .puml.
To generate an SVG (PNG is the default) use the following command: java -jar <path/to/plantuml.jar> --svg <my/diagram.puml>

@startuml
  zeroOrOne |o--|| exactlyOne
  exactlyOne ||--o{ zeroOrMany
  zeroOrMany }o--|{ oneOrMany
  oneOrMany }|--o| zeroOrOne
@enduml