POSC Specifications
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Logical Dictionary Conventions |
How to Read the Epicentre Logical Dictionary
The dictionary report provides the complete description of the logical data model.
The dictionary report format is used to describe regular entities, reference entities
and properties. In addition to this dictionary report, the data model is available
as a set of EXPRESS text files.
The report provides details about inherited and direct attributes (relationships
are types of attributes) and rules for each entity. This report style gathers all
relevant information about an entity into one description and allows inherited
information to be repeated throughout the report.
The general report style is:
ENTITY_NAME (abstract) (Fixed|Open|Local) (C###) |
(Rules) (Express) |
Description of the entity.
- attribute_name (ATTRIBUTE QUALIFIERS: (AGGREGATE[#:#])related_entity(paired attribute)|ndt) Attribute description. (Inherited from supertype_entity_1).
- Local rules: - Uniqueness constraint attribute_1, attribute_2,..
- Supertype path(s): - supertype_entity_1 > supertype_entity_2 > entity_name.
- Referenced in Diagrams: AA#: Diagram name
Entities
Supertype entities are marked as (abstract) or left with no annotation if non-abstract. In the POSC methodology, only an instance of a non-abstract supertype entity can exist independently. Entities containing standard POSC instances are designated as either (Fixed) or (Open).
- (Fixed) means that the complete population has been specified by POSC, while
- (Open) says that additions not specified by POSC are allowed,
- (Local) means that POSC has not defined any standard instances. Selecting the (Fixed | Open ) characters after the entity name will cause Browser to jump to the population of standard instances provided by POSC. For a reference entity defined as (Local), there will be no population of standard instances, and therefore no link.
- The (Rules) link takes you to the start of the rules that are defined for this entity. This is a useful way to get to see the information given at the end of each entity definition, especially when the entity contains many direct and inherited attributes.
- The (Express) link takes you to the EXPRESS definition of this entity.
Changes
Changes to Epicentre from the previous version have been allocated change numbers.
If an entity, attribute or rule has changed from the previous version, this will
be shown by a change number(s) in parentheses (with each number prefaced by "C").
This number is a link that takes you to the Incremental Express change.
Attributes
A standard relational table has only single-value attributes. For example, a standard relational table may have two attributes, such as latitude and longitude. POSC's methodology and report format allows multi-value attributes. For example, the attributes latitude and longitude are replaced in POSC's methodology by the attribute location. This attribute points to a named defined type, Ndt_location which carries two values instead of one.
An attribute (when representing a relationship) can also point to another entity. In the previous example, the attribute may point to a vertex instead of pointing to a location. This makes it possible to share the location of a point through a vertex between several business objects. The attribute may also point to several instances of an entity. For example, a well may point to several instances of wellbore. An aggregate is defined (bag, set, list or array) to specify the type of relationship with the target entity. These types of attributes are equivalent to classical relationships and are shown on the diagrams as classical relationships.
Following the attribute name in parentheses, is a list of attribute qualifiers, separated by commas, and terminated by a colon, which have the following meanings:
- I -The attribute is inherited from one of the entity's supertypes. Inherited attributes can be referenced directly through the API as regular attributes. For example, a Geologic_feature has an attribute Geologic_province. One of its subtypes is a Rock_feature. The entity Rock_feature has no attribute Geologic_province, but one can query the geologic province of a Rock_feature, as it is inherited from its supertype, Geologic_feature.
- K -The attribute is a key. A combination of all the key attributes of an entity is called the entity's secondary identifier (SI). These attributes are expected to be used preferentially for recognizing the real world thing the instance represents. The component(s) of a SI may be optional or mandatory. When all the components are mandatory, the model requires uniqueness of the SI in the entity.
- M -The attribute is mandatory. A mandatory attribute cannot be null or missing for a valid instance of the entity.
- O -The attribute is optional
- V -The attribute represents an inverse relationship
If the attribute represents a relationship, following the attribute qualifiers will be an indication of the cardinality when there is a potential for more than one instance per attribute (an aggregate). The types of aggregate are: bag, set, list and array. The lower bound of the aggregate is the first value in the square brackets and the upper bound is the second value.
The next parenthesized item for the attribute is the named defined type or entity to which the attribute is related. Special naming conventions have been used for the following:
- named defined types are prefixed with "Ndt_",
- reference entities with "Ref_" and
- properties with "Pty_".
Selecting the italicized entity (including "Ref_" and "Pty_ ") or the named defined type will cause Browser to jump to the designated dictionary location.
The last parenthesized item for the attribute only occurs for attributes that are related to an entity - this item is the name of the corresponding attribute in the related entity - in EXPRESS terms, it is the corresponding forward attribute if this is an inverse attribute, and the inverse attribute if this the forward attribute.
The final documentation item is a description of the attribute.
Rules
Rules that influence the behavior of an entity, its attributes, and relationships are shown below a solid line that separates the rules from the attributes. If the entity is a supertype, the entities that are its subtypes are listed here. Selecting a subtype entity from this list will cause Browser to jump to that entity.
Supertype path
The report next indicates which entities are the direct and indirect supertypes of the entity. Indirect supertypes are the supertypes of the direct supertypes. The supertype entities are listed with the highest level first, followed by its immediate subtype and so on, until the current entity is reached. Again, selecting an entity from these lists will cause Browser to jump to the dictionary report for the entity.
Referenced in Diagram
The paragraph "Referenced in Diagrams:" displays the list of diagrams in which the entity is displayed. Selecting one of these will cause Browser to jump to the appropriate diagram.
Named Defined Type Report Conventions
Named Defined Type (Ndt) is used to describe the structures and representations of attributes in Epicentre. As each Ndt is presented, the name is given in boldface type. The definition immediately follows.
The parameters of the Data Types are listed in a table below the Ndt description. The significance of the Ndt parameters is described in the Methodology section. Most of the parameters are linked into the dictionary reports for data type behavior or standard instances.
Reference Entities Report Conventions
The reference entities used in Epicentre do not normally appear on the data model diagram. Reference entity names begin with the characters "Ref_" followed by a name indicating the use of the reference entity. Reference entities are described as Regular Entities.
Following the description of the structure of the reference entities, this document includes the populations of POSC Open and POSC Fixed reference entities. Populations of Local reference entities will not be defined by POSC.
Selecting either (fixed) or (open) after the entity name will cause Browser to jump to the standard instances defined for the reference entity.
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