Houdini no longer has SHOP networks. Materials are now built from pure 
VOPs.
Nodes
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Channel nodes create, filter, and manipulate channel data.
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Composite nodes create, filter, and manipulate image data.
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Dynamics nodes set up the conditions and rules for dynamics simulations.
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Object nodes represent objects in the scene, such as character parts, geometry objects, lights, cameras, and so on.
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Render nodes either render the scene or set up render dependency networks.
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Geometry nodes live inside Geo objects and generate geometry.
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Containers for VOP networks.
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VOP nodes let you define a program (such as a shader) by connecting nodes together. Houdini then compiles the node network into executable VEX code.
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TOP nodes live inside TOP objects and do work.