Geodatabase Relationships

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Geodatabase Relationships Relationship Classes

• GIS 458
• Spring 2006
• Larry Clamp

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Geodatabase Relationships

• Relationships are associations between
  geodatabase objects
• Can exist between spatial objects
• Features in feature classes
• Can exist between non-spatial objects
• Rows in tables

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Major Types of Relationships

• Topological
• Built into data when networks or topologies are
  built
• Spatial
• Operations that help determine locations
• Intersect, coincidence, overlap, inside of
• General
• Explicitly defined to form a persistent tie
  between objects
• Our topic tonight

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Relationship Classes

• Feature Classes Spatial Objects
• Tables Non-Spatial Objects
• Relationship Classes Relationships

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Relationship Classes

• Link objects between classes in GDB
• All combinations of tables FCs supported
• RCs are persisted in GDB
• Joins relates only in map document
• Have advanced capabilities
• Read-write access
• All cardinalities
• Simple or composite
• Relationship rules
• Referential integrity
• Versioning supported

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Advanced Capabilities

• Read-write access
• Can edit attributes in related classes
• All cardinalities
• 1-1, 1-many, many-many
• May have attributes
• Simple or composite
• Simple peer-to-peer
• Composite parent-to-child
• Relationship Rules
• Rules to refine cardinality based on subtypes
• Referential integrity
• Performs cascade delete
• Versioning supported
• Allows multiple users in ArcSDE environment

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Table Relationships

• One is the Origin
• One is the Destination the one linked to
• Key Fields
• Matching or linking fields in both tables
• May have different names
• Must be of same data type
• Origin Primary Key
• Key field in origin class
• Destination Foreign Key
• Key field in destination class

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Relationship Class Properties

• Name
• Labels
• Type
• Cardinality
• Notification
• Origin/Destination Classes
• Key Fields

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Names Labels

• Relationship Class names must be unique in the
  GDB
• Relationships may be navigated either direction
• Each end need a label for navigation
• Labels must be unique only for relationship, not
  GDB
• Visible in ArcMap
• Should describe the nature of the relationship

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Type

• Determines how referential integrity is enforced
• Simple
• Peer-to-Peer
• Related objects exist independently
• Composite
• Parent-child
• Existence of destination objects controlled by
  origin
• Delete origin (parent) and destination (child)
  ceases to exist
• Spatial effect
• Moving or rotating origin moves or rotates
  destination
• Feature linked annotation is an example

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Cardinality

• Number of objects in origin that are related to a
  number of objects in destination
• One-to-one
• One origin object to one destination object
• A parcel can have only one legal description
• Also covers many-to-one
• One origin object still only matches one
  destination
• One-to-many
• One origin object can relate to many destination
  objects
• A parcel can have many buildings
• Many-to-many
• One origin object can relate to multiple
  destination objects
• One destination object can relate to many origin
  objects
• A property can have many owners and an owner can
  have many properties

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Many-to-Many

• Requires an intermediate key table
• Associate key values between classes
• ArcGIS generates the fields
• User populates records
• May choose to store attributes about the
  relationship
• i.e. percentage of ownership

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Relationship Messages

• Primarily used by programmers
• AKA Notification
• Related objects notify each other when they are
  changed
• Can control behavior of composite relationships
• Have no effect on simple relationships
• Choices
• None Cascade delete, no feature following
• Forward Cascade delete, feature following, and
  annotation update
• Backward Cascade delete, no feature following
• Both Cascade delete, feature following, and
  annotation update

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Relationship Rules

• Rules make cardinality more specific
• Set between subtypes
• Can make some relationships illegal
• Help maintain integrity in the geodatabase

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Setting Rules

• In the properties of an existing relationship
  class
• Set between subtypes
• If one rule is set, then others must also be set
• No set rule invalid relationship

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Referential Integrity

• RI manages values of keys fields
• Choice of origin and destination is important
• When you delete a record in origin, the RC finds
  related records in destination and sets value of
  key field to Null
• Incorrect choice may damage database

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RI Examples

• Case 1 WRONG
• Parcel (origin) to Zoning (destination)
• Delete a parcel and the corresponding zone key
  field is set to Null
• Other parcels that have that zoning code no
  longer have a match
• Case 2 RIGHT
• Zoning (origin) to Parcel (destination)
• Delete a parcel and there is no effect on the
  zoning
• Deleting a zoning code sets parcel key field to
  Null, which is how it should be
• It needs to be re-zoned

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Creating Relationship Classes

• ArcCatalog context menu
• Specify name, participating classes, type,a nd
  other properties
• Geoprocessing framework
• ArcToolboxgtData Management Tools
  toolboxgtRelationship Classes toolset

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Relationship Classes in ArcMap

• Use them to
• Query
• Analyze
• Edit
• Make Reports
• Can view properties of all related objects
• To label or symbolize using related records, a
  join is required
• Join based on relationship class