Figure 1 A typical solid model
If you consider wireframe model as the skeleton of an object, surface model can be the external shell, and solid model can represent the internal structure of such object. With more information defined, solid model solves many constraints inherent to surface model. Solid modeling is therefore widely recognized as the way to serve as an integrated modeling for design, analysis, documentation, and manufacturing.
The first generation of solid modeling systems tackles the technical issues in defining 3D geometry with volume information. As technology advances, new generations of solid modeling systems are developed to suit users native way of thinking and description in design process. The new modelers are improved from geometric oriented solid modelers to allow more flexible modification while retaining accurate modeling. They communicates in higher level language and associates operations directly with objects instead of the coordinate system. The systems also assists design for manufacturing by addressing design intents in dimension, geometry, relationship, and feature and attains higher data associativity.