Introduction

ISO 10303 is an International Standard for the computer-interpretable representation of product information and for the exchange of product data. The objective is to provide a neutral mechanism capable of describing products throughout their life cycle. This mechanism is suitable not only for neutral file exchange, but also as a basis for implementing and sharing product databases, and as a basis for retention and archiving.

This part of ISO 10303 specifies an application module for the representation of shape elements that are derived from other shape elements. It provides a general means for specifying a set of points as having been derived from elements of a the shape of a part.

The derived shape element has a deriving relationship to another shape element. The deriving relationship can exist between shape elements that participate in the specification and verification of geometric dimensions and tolerances that are imposed as requirements on the product shape.

EXAMPLE 1   The axis of a hole can be derived from the cylindrical surface of the hole.

The outputs of operations of specification and verification can be related to the inputs.

EXAMPLE 2   The following are examples of operations used in the verification or specification of product shape.

• creating a cross section curve by intersecting a plane and a feature;
• mathematically fitting a circle to a cross section;
• calculating the center point of a circle;
• collecting points to form a locus.

The classification and definition of such operations is outside the scope of this part of ISO 10303.

This part of ISO 10303 does not limit the use of deriving relationships between shape elements any particular application context.

EXAMPLE 3   The geometry of derived shape elements is construction geometry, and the geometric construction operations can be used in creating the geometry that represents a derived shape element.

A derived shape element need not have a representation.

EXAMPLE 4   A hole is a shape element that is represented by a non uniform rational b-spline surface that is cylindrical. The axis is specified as a derived shape element, but with no explicit representation. A straightness tolerance is applied to the axis of a hole.

Clause 1 defines the scope of the application module and summarizes the functionality and data covered. Clause 3 lists the words defined in this part of ISO 10303 and gives pointers to words defined elsewhere. The information requirements of the application are specified in Clause 4 using terminology appropriate to the application. A graphical representation of the information requirements, referred to as the application reference model, is given in Annex C. Resource constructs are interpreted to meet the information requirements. This interpretation produces the module interpreted model (MIM). This interpretation, given in 5.1, shows the correspondence between the information requirements and the MIM. The short listing of the MIM specifies the interface to the resources and is given in 5.2. A graphical representation of the short listing of the MIM is given in Annex D.

In ISO 10303, the same English language words can be used to refer to an object in the real world or concept, and as the name of an EXPRESS data type that represents this object or concept.

The following typographical convention is used to distinguish between these. If a word or phrase occurs in the same typeface as narrative text, the referent is the object or concept. If the word or phrase occurs in a bold typeface or as a hyperlink, the referent is the EXPRESS data type.

The name of an EXPRESS data type can be used to refer to the data type itself, or to an instance of the data type. The distinction between these uses is normally clear from the context. If there is a likelihood of ambiguity, either the phrase "entity data type" or "instance(s) of" is included in the text.

Double quotation marks " " denote quoted text. Single quotation marks ' ' denote particular text string values.

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