How To Read a Relational Data Model

Many types of information are shown in the data model diagrams:

• Table Names
• Attributes
• Name
• Data type (text, number, date)
• Required (NN = Not Null) or not required in the table (this may be different than methodologically required)
• Keys:
• Primary key (PK) - value which uniquely identifies every row in the table.
• Foreign keys (FK) - values match a primary or alternate key inherited from some other table.
• Alternate Keys (AK) - key associated with one or more columns whose values uniquely identify every row in the table, but which is not the primary key
• Primary Foreign Key (PFK) - key which acts as primary key in more than one table which occurs in tables with an identifying relationship.
• Relationships
• Which tables are related
• Cardinality of relationships
• Required vs. optional relationships

Key to Tables and Attributes

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Key to Relationships

A dashed line between tables indicates a non-identifying relationship. This means that each table has its own unique identifier (primary key) and does not inherit it from the other table. Instead, the primary key of one table becomes a foreign key in the other.

In the example above SYNONYM_GLOBAL is an intersection table between ELEMENT_GLOBAL and SCIENTIFIC_NAME. It is necessary to "resolve" the many-to-many relationship between these tables for synonyms (that is, an element may have many synonyms, and the same synonym may apply to more than one element.

A solid line indicates an identifying relationship. This means that two tables share the same primary key. One type of identifying relationship is between a main table and its subtypes, as in the example shown below:

These subtypes means that every item in the HIGHER_CLASS_UNIT table must be either a TAXON or a COMMUNITY, but can't be both

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Related Topics:

• Biotics 4 Data Model
• Biotics 5 Data Model
• Data Model Details Overview

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