Node graph architecture
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Node graph architecture is a type of software design which builds around modular node components which can be connected to form a graph. Often the software's underlying node graph architecture is also exposed to the end user as a two-dimensional visualization of the node graph. The node graph architecture is popular in the film and computer games industry.
There are often many different node types participating in the node graph. For example in the Nuke Manual[dead link] they list hundreds of nodes. Each node type performs one specific task. For example Nuke's Merge node produces an output image in which a number of input images have been layered. By connecting many different node types together complex image effects can be produced.
The node graph architecture often allows grouping of nodes inside other group nodes. This hides complexity inside of the group nodes, and limits their coupling with other nodes outside the group. This leads to a hierarchy where smaller graphs are embedded in group nodes. In Nuke the group node is simply called the Group node.
In the paper Hierarchical Small Worlds in Software Architecture they argue that most large software systems are built in a modular and hierarchical fashion, and they use node graphs to analyze large software systems. In fact a large number of software analysis papers often use node graphs to analyze large software systems suggesting that node graphs are good models of the internal structure and operation of the software.
Many commercial and non-commercial software systems allow users to visualize and interact with internal components via the node graph. Below are a number of node graph based software applications from the film and games industry.
Nuke is a compositing application for film made by The Foundry. The nodes in its graph can be connected to produce complex 2D image processing effects.
Houdini is a procedural modelling, animation, and rendering application made by Side Effects Software. The nodes in its graph produce procedural geometry. Side Effects Software refers to their node graphs as networks.
Valve's Source SDK allows players to create custom maps for all of their games. The nodes in its graphs are used in AI path planning and also in sending signals between game entities.
Nodality is a free node based image editing and compositing application for iPad.
Open source applications
Blender is a modelling, animation, compositing, and rendering application. The nodes in its graph produce images, 3D geometry, and various other attriutes.
NodeBox is procedural image creation application. The nodes in its graph produce vector based images.
In-house studio applications
Many large movie studios are rumored to be using the node graph architecture to design many of their in-house software tools. Sony Pictures Imageworks uses an in-house compositing and lighting tool called Katana. In a recent press release (November 2009) it was announced that the Sony Pictures Imageworks' Katana software would be integrated into The Foundry's Nuke software.
- Hierarchical Small Worlds in Software Architecture
- Metrics of Software Architecture Changes Based on Structural Distance
- Graph Grammars and Constraint Solving for Software Architecture Styles. CiteSeerX: 10.1.1.108.9362.