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The Characteristics Schema
| Overview |
It became clear during the creation of the NPDM that there is an enormous amount of data which is covered by the existing legacy standards that is attached to the key ideas of product, anomaly and task (and the relationships between them). The data provides for many characteristic values, varying from the familiar ideas, such as mean time between failure to much more obscure values.
Furthermore many of these are provided twice (in the LSAR), once as a requirement (from the assumed single customer) and later as a predicted value (provided by the system/equipment supplier). However in the NPDM, these values can be specified as requirements by different organizations (i.e. applying in a different scenario). Furthermore, taking a view that goes through the life of the product, a measured value (based on fact rather than prediction) may also be provided.
| Description |
It became clear during the creation of the NPDM that there is an enormous amount of data which is covered by the existing legacy standards that is attached to the key ideas of product, anomaly and task (and the relationships between them). The data provides for many characteristic values, varying from the familiar ideas, such as mean time between failure to much more obscure values.
Furthermore many of these are provided twice (in the LSAR), once as a requirement (from the assumed single customer) and later as a predicted value (provided by the system/equipment supplier). However in the NPDM, these values can be specified as requirements by different organizations (i.e. applying in a different scenario). Furthermore, taking a view that goes through the life of the product, a measured value (based on fact rather than prediction) may also be provided.
Given the potential number of such characteristics (see the combined data element lists of the legacy standards), the NPDM takes a more general approach. Firstly a characteristic (or one of many subtypes) is used. In general terms, this defines a name, description and value.
Figure 8.1 General form of characteristic
This is then assigned using a characteristic_assignment entity that allows the following to be defined:
- who provided the value
- what scenario does it apply to
- is it measured, required, planned, allocated or calculated
- to what does it apply
Figure 8.2 Characteristic assignment
Additionally, some characteristics may be qualified as being mean, maximum or minimum values. This is done by using a qualified_characteristic_assignment entity with an additional attribute that allows the value to be qualified as being a "mean" value for example.
By using this approach the NPDM is kept as an open model which can easily be extended as additional characteristics can be added.
Currently there are many different specific characteristics defined as subtypes of the characteristic entity. If we look at one example to see the way these work, most of the subtypes will become clear.
Mean time between failure is a typical characteristic. It applies to a product (in the NPDM, a product_design_definition or an element) and may be specified as a requirement or as a predicted value by a supplier. In the NPDM this will be a qualified assignment (as "mean") of the time_between_failure characteristic.
