DGML

DGML (Directed Graph Markup Language) is an XML-based file format for directed graphs, developed by Microsoft and first shipped in September 2009 with Visual Studio 2010. It uses the namespace http://schemas.microsoft.com/vs/2009/dgml/, carries the .dgml file extension, and is best known as the on-disk persistence format for Visual Studio "code maps" — dependency graphs that visualize how classes, assemblies, namespaces, and other source components relate to one another. It supports both cyclic and acyclic graphs.

Structurally, a DGML document has a single root DirectedGraph element containing optional child collections. Nodes holds Node elements (each with an Id and usually a Label); Links holds Link elements that connect a Source node to a Target node, giving the graph its directed edges. Beyond this core, DGML is notably rich in annotation and presentation metadata. A Categories section defines named Category elements used to group nodes and links; a Properties section declares typed custom properties (String, Brush, DateTime, Boolean, and others) that can be attached to any element; and a Styles section defines conditional visual rules — for example, coloring a node green when a "Passed" property equals True. Nodes can also be nested to represent containment/grouping, and the graph can carry layout hints (Sugiyama tree, ForceDirected, DependencyMatrix, or none) plus flow direction.

In the format-conversion landscape, DGML occupies a similar niche to other XML graph interchange formats such as GraphML, GEXF, XGMML, and GXL, and to the DOT language of DOT, but it is tightly coupled to the Microsoft/Visual Studio toolchain rather than being a vendor-neutral standard. Its strengths are a clean, IntelliSense-friendly XML schema, first-class support for user-defined typed properties, categories, and conditional styling, and strong tooling inside Visual Studio for generating and browsing large code maps. Libraries such as DgmlPowerTools, dgml2, and the DgmlBuilder .NET library help produce and manipulate DGML programmatically.

Its main limitations are ecosystem lock-in: authoring and interactive viewing traditionally required Visual Studio (specific code-map features were Enterprise-edition only), third-party viewers exist but are less complete, and adoption outside the .NET world is limited. The format also has no widely used streaming or binary variant, so very large graphs are constrained by verbose XML.