## 5 Applications of markup in Engineering Design
### 3D annotation and markup in engineering design  
With the wider applications of 3D models in industry, 3D annotations and markups appeared and are playing a more and more important role. The first exploration focuses on whether the annotations and markups can help integration of product models with information that has historically been difficult to represent unambiguously and pictorially (such as the information required for manufacturing a product - tolerances, machining processes, surface finishes), using formally specified systems of symbols normally recorded in some level of standard. The American Society of Mechanical Engineers (ASME) Y14.41 [56] issued in 2003 is one such standard. Other typical examples of early research work include: [PERSON] and [PERSON] [57], who used a graph to represent machining features, whose nodes and edges corresponding to features and its relationships of features. The nodes and edges are annotated with labels by various parameters that may be useful for classification purposes. [PERSON] and [PERSON] [58] proposed an architecture for a product master model federating CAD systems with downstream application processes for different feature views and especially addressed the need to make persistent associations of design information with net shape elements. With the high demands of 3D annotations, recently, CAD/CAM packages have introduced 'annotation' support. For examples, AutoCAD 2008 offers an automatically scaled annotation capability [59]; SolidEdge V19 supports the ASME Y14.41 standards for 3D annotation [60]; Pro/ENGINEER provides annotations of dimensions, tolerances, surface finish, _etc._[61]; NX5 allows users to create annotation manufacturing information [62]; CATIA V5R13 supports creation of annotation like tolerance information [63]; and annotation tools were firstly introduced in MicroStataion TriForma version 8 [64]. However, to sufficiently support engineering design process and capture the rationale behind it, a number of limitations need to be overcome:* The 'annotation' functions provided are often limited to a single type (e.g. free-text, Uniform Resource Identifier (URI) or numerical format), they cannot satisfy the requirements of annotation schemes supporting context-specific information and multiple viewpoints. * The content of the annotation is associated with specific product models. In other words, the annotation adopts 'inline' annotation strategy. This is easy to accomplish, but it does actually change the models, and it is only reusable for invariant topologies. * It is difficult to place multiple independent sets of annotation in the same model, which hinders the annotation being re-organized and retrieval at later stage. Thus, an extension to existing 'annotation' functions in the commercial packages is really needed. Some researchers (e.g. [14]) have explored the possibility of using '_stand-off_' methods on the CAD models, which means that the annotation is stored in a separate external document utilizing a system of references or pointers to indicate the element (such as a face, or a feature within a CAD model) to which the annotation refers. For example, [PERSON] _et al._[14] discussed the techniques of'stand-off' markup on the 3D model, identified the key issue for the implementation - persistent identification of geometry, proposed an approach called LIghtweight Model with Multi-layer Annotation (LIMMA), and finally demonstrated its support for multiple viewpoints within a CAD model. As the same annotation file can be applied to any copy of the model in any format, the annotation information can be independent from the model format and shared by various users. It is important that all users can contribute their experiences and knowledge by separate annotation rather than by editing the CAD models directly. Therefore, besides the advantages mentioned in the Section 4, the'stand-off' method has potential in support of knowledge sharing throughout a product's lifecycle.