Database Reference
In-Depth Information
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Domain of values of each attribute becomes the domain for the corresponding
data field.
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A single-valued or derived attribute is transformed into a single field.
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For a composite attribute, as many fields are used in the segment type as the
number of component attributes in the composite attribute.
Instance Identifiers
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The attribute or attributes forming the instance identifier maps into a set of
fields termed the key of the record type.
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Record occurrences may be sorted based on the values of the key fields.
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No special significance is attached to the key fields as all navigation within the
data model is through physical pointers.
Relationships
Each relationship in the network data model becomes a binary
link between the owner and the member record types.
One-to-One or One-to-Many Relationship
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For each object set in the semantic data model, create a record type.
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If two object sets A and B are in a one-to-one or one-to-many relationship,
connect them with A as the owner record type and B as the member record
type.
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The object set on the “one” side of the relationship becomes the owner record
type and the object set on the “many” side of the relationship becomes the
member segment type.
Many-to-Many Relationship
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For each object set in the semantic data model, create a segment type.
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If two object sets A and B are in a many-to-many relationship, map this as two
one-to-many relationships.
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Create a link record type C to contain key values of both A and B.
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Define two sets, one with A and the link record type C, the other with B and
the link record type C.
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The set with A as the owner record type and C as the member record type
represents one of the transformed one-to-many relationship. The set with B as
the owner record type and C as the member record type represents the other
transformed one-to-many relationship.
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