Basic Terminology in Library Information Systems
LRM Terminology
LRM Module 2
Standing Committee on Training
Program for Cooperative Cataloging (PCC)
March 2020
Basic Terminology—Overview
•
All definitions* taken from LRM Chapter 7, Glossary of Modelling
Terminology
•
Vocabulary mostly originates from the entity-relationship model
•
Some vocabulary familiar from FRBR, but be cautious—it may be
somewhat differently defined
* Except Inheritance
2
Terminology Covered in this Module
•
Class
•
Entity
•
Superclass
•
Subclass
•
Disjointedness
•
Property
•
Attribute
•
Relationship
•
Inheritance
•
Domain
•
Range
•
Reification
3
Class
•
LRM gives no formal definition for class, although the term is used
often
•
Here are some definitions from common usage and from the RDF
schema:
•
“A group, set, or kind, sharing common attributes” (
Merriam-Webster
)
•
“Resources may be divided into groups called classes. The members of a
class are known as
members
of the class” (
RDF Schema 1.1
)
•
The class concept is inherent to the enhanced entity-relationship
model, but not part of a basic entity-relationship model
4
Entity
An abstract class of conceptual objects, representing the key objects of
interest in the model
… that is, “the key objects of interest to users of library information systems.”
(LRM 4.1.1.)
•
Entities
are treated as classes in LRM; the term
entity
tends to be used mostly
for the LRM entities, while
class
is used for non-RDA entities and descriptions of
LRM entities. Other Modules will define and explain specific LRM
entities
.
•
The primary benefit of treating
entities
as classes is that it also introduces the
relational concepts of
superclass
and
subclass
5
Class relationships--Superclass
•
An entity may group several entities/classes together in a superordinate class, a
more general class under which a set of more specific classes is incorporated.
This is known in LRM as a
superclass.
Example:
The entity
Agent
is the superclass of the
entities
Person
and
Collective Agent
6
Class relationships--Subclass
Multiple entities may be grouped into a superordinate entity, if all their instances
are instances of that larger entity. This is known as a
subclass.
The LRM definition
is:
“An entity, all of whose instances are also instances of a larger, superordinate
entity.”
The relationship is described as an “isA” relationship
Example:
The entities
Person
(an individual) and
Collective
Agent
(a group) are subclasses of the entity
Agent
.
Person
“isA”
Agent
Collective Agent
“isA”
Agent
7
Entity Hierarchy: Superclass, Class,
Subclass
(IFLA Library Reference Model, August 2017, as amended and corrected through December 2017 (IFLA LRM (2017-12))
8
Disjoint Entities
Entirely non-overlapping sets. Disjoint entities can have no instance
that is simultaneously an instance of more than one of these entities
“IFLA LRM declares that, other than those entities related by the
“isA” hierarchies, the entities in the model are disjoint.” (IFLA LRM
(2017-12) 5.2)
9
Disjointness is easy!
Some examples of disjointness are easily understandable.
For example, something cannot be both an instance of the
person
entity and an instance of the
collective agent
entity.
These entities have an “isA” relationship to the entity
agent
, but they
are disjoint to each other.
(cannot be a)
10
Maybe not always easy.
Disjointness is less obvious but equally important when something is considered in
different aspects.
For example:
Hamlet
as
work
,
expression
,
manifestation
, and
item
: all may share
the same
nomen string
(can be referred to by the same name) but are nonetheless
different and
disjoint
entities
11
Property, Attribute,
Relationship
Property:
An attribute or relationship of an entity
Attribute:
A type of data which characterizes specific instances of an entity
Relationship:
A connection between instances of entities
Attributes
and
Relationships
are discussed more fully in subsequent modules.
12
Inheritance
Definition:
Modeling in which an entity or class automatically acquires all the attributes
and relationships from its superclass.
Example:
The
Agent
entity has the following attributes:
■
Contact information [LRM-E6-A1]
■
Field of activity [LRM-E6-A2]
■
Language [LRM-E6-A3]
The
Person
entity “inherits” these attributes and adds the following attribute:
■
Profession/Occupation [LRM-E7-A1]
13
Properties--Inheritance
•
Any property (
relationship
or
attribute
) that applies to a
superclass
also applies to all entities of its
subclasses
•
Example:
Any relationship or attribute that applies to the entity
Agent
also
applies to the entity
Person
(a subclass of
Agent
), and therefore does not
need to be specifically declared for
Person
•
The entity
Agent
has the
attribute
Language, defined as “A language used by the
agent
when
creating an
expression
.” The entity
Person
is a subclass of the entity
Agent
and therefore also
has the attribute Language
•
The
relationship
“is member of” is defined for the entity
Agent
. It also applies to the entity
Person
, which is a subclass of the entity
Agent
14
Relationships--Domain & Range
Domain:
The source entity, or departure point, for a relationship
Range:
The target entity, or arrival point, for a relationship
To use a grammatical analogy,
Domain
and
Range
can be thought of as
the subject and object, respectively, of a relationship.
15
Domain & Range
For example:
In the relationship “
Work
‘is realized through’
Expression
,” Work is the
domain
and
Expression is the
range
.
In the inverse relationship “
Expression
‘realizes’
Work
,” Expression is the
domain
and Work is the
range
.
Domain
and
Range
are revisited in later modules
16
Reification
•
Process through which a relationship is modelled as an entity, so
that it can in turn have its own attributes and relationships
In non-technical English, to reify is “To regard or treat (an abstraction) as if it
had concrete or material existence. [Latin
rēs
,
rē-
, thing … + fy.] (
American
Heritage Dictionary
, third edition.)
Reification in LRM is just a specialized instance of this. Relationships are not
entities in LRM, but treating them as if they were allows them to be more fully
described and discussed (as in Table 4.7 and the detailed definition in 4.3.3).
•
Reification is further discussed in later modules
17
Explore key terminology like Class, Entity, Superclass, Subclass, and more from the LRM Module. Learn about the definitions and relationships of these essential concepts in the context of library information systems.
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Presentation Transcript
LRM Terminology LRM Module 2 Standing Committee on Training Program for Cooperative Cataloging (PCC) March 2020
Basic TerminologyOverview All definitions* taken from LRM Chapter 7, Glossary of Modelling Terminology Vocabulary mostly originates from the entity-relationship model Some vocabulary familiar from FRBR, but be cautious it may be somewhat differently defined * Except Inheritance 2
Terminology Covered in this Module Class Attribute Entity Relationship Superclass Inheritance Subclass Domain Disjointedness Range Property Reification 3
Class LRM gives no formal definition for class, although the term is used often Here are some definitions from common usage and from the RDF schema: A group, set, or kind, sharing common attributes (Merriam-Webster) Resources may be divided into groups called classes. The members of a class are known as members of the class (RDF Schema 1.1) The class concept is inherent to the enhanced entity-relationship model, but not part of a basic entity-relationship model 4
Entity An abstract class of conceptual objects, representing the key objects of interest in the model that is, the key objects of interest to users of library information systems. (LRM 4.1.1.) Entities are treated as classes in LRM; the term entity tends to be used mostly for the LRM entities, while class is used for non-RDA entities and descriptions of LRM entities. Other Modules will define and explain specific LRM entities. The primary benefit of treating entities as classes is that it also introduces the relational concepts of superclass and subclass 5
Class relationships--Superclass An entity may group several entities/classes together in a superordinate class, a more general class under which a set of more specific classes is incorporated. This is known in LRM as a superclass. AGENT (entity) Example: The entity Agent is the superclass of the entities Person and Collective Agent Is a superclass of COLLECTIVE AGENT (entity) PERSON (entity) 6
Class relationships--Subclass Multiple entities may be grouped into a superordinate entity, if all their instances are instances of that larger entity. This is known as a subclass. The LRM definition is: An entity, all of whose instances are also instances of a larger, superordinate entity. The relationship is described as an isA relationship AGENT (entity) Example: Is a subclass of The entities Person (an individual) and Collective Agent (a group) are subclasses of the entity Agent. COLLECTIVE AGENT (entity) PERSON (entity) Person isA Agent Collective Agent isA Agent 7
Entity Hierarchy: Superclass, Class, Subclass (IFLA Library Reference Model, August 2017, as amended and corrected through December 2017 (IFLA LRM (2017-12)) 8
Disjoint Entities Entirely non-overlapping sets. Disjoint entities can have no instance that is simultaneously an instance of more than one of these entities IFLA LRM declares that, other than those entities related by the isA hierarchies, the entities in the model are disjoint. (IFLA LRM (2017-12) 5.2) ENTITY A ENTITY B IS DISJOINT WITH 9
Disjointness is easy! Some examples of disjointness are easily understandable. For example, something cannot be both an instance of the person entity and an instance of the collective agent entity. COLLECTIVE AGENT (entity) PERSON (entity) IS DISJOINT WITH (cannot be a) These entities have an isA relationship to the entity agent, but they are disjoint to each other. 10
Maybe not always easy. Disjointness is less obvious but equally important when something is considered in different aspects. NOMEN STRING: HAMLET ITEM (entity) WORK (entity) EXPRESSION (entity) MANIFESTATION (entity) IS DISJOINT WITH IS DISJOINT WITH IS DISJOINT WITH For example: Hamlet as work, expression, manifestation, and item: all may share the same nomen string (can be referred to by the same name) but are nonetheless different and disjoint entities 11
Property, Attribute, Relationship Property: An attribute or relationship of an entity Category attribute: Novel Representative Expression attribute: English WORK (entity) Attribute: A type of data which characterizes specific instances of an entity TIME-SPAN (entity) BOOK (entity) Relationship: WAS PUBLISHED A connection between instances of entities Attributes and Relationships are discussed more fully in subsequent modules. 12
Inheritance Definition: Modeling in which an entity or class automatically acquires all the attributes and relationships from its superclass. Example: The Agent entity has the following attributes: Contact information [LRM-E6-A1] Field of activity [LRM-E6-A2] Language [LRM-E6-A3] The Person entity inherits these attributes and adds the following attribute: Profession/Occupation [LRM-E7-A1] 13
Properties--Inheritance Any property (relationship or attribute) that applies to a superclass also applies to all entities of its subclasses Example: Any relationship or attribute that applies to the entity Agent also applies to the entity Person (a subclass of Agent), and therefore does not need to be specifically declared for Person The entity Agent has the attribute Language, defined as A language used by the agent when creating an expression. The entity Person is a subclass of the entity Agent and therefore also has the attribute Language The relationship is member of is defined for the entity Agent. It also applies to the entity Person, which is a subclass of the entity Agent 14
Relationships--Domain & Range Domain: The source entity, or departure point, for a relationship Range: The target entity, or arrival point, for a relationship To use a grammatical analogy, Domain and Range can be thought of as the subject and object, respectively, of a relationship. DOMAIN (SUBJECT) RELATIONSHIP (VERB) RANGE (OBJECT) 15
Domain & Range For example: In the relationship Work is realized through Expression, Work is the domain and Expression is the range. WORK (DOMAIN) EXPRESSION (RANGE) IS REALIZED THROUGH In the inverse relationship Expression realizes Work, Expression is the domain and Work is the range. EXPRESSION (DOMAIN) WORK (RANGE) REALIZES Domain and Range are revisited in later modules 16
Reification Process through which a relationship is modelled as an entity, so that it can in turn have its own attributes and relationships In non-technical English, to reify is To regard or treat (an abstraction) as if it had concrete or material existence. [Latin r s, r -, thing + fy.] (American Heritage Dictionary, third edition.) Reification in LRM is just a specialized instance of this. Relationships are not entities in LRM, but treating them as if they were allows them to be more fully described and discussed (as in Table 4.7 and the detailed definition in 4.3.3). Reification is further discussed in later modules 17
