LRM Terminology LRM Module 2 Standing Committee on

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. AGENT (entity) Example: The entity Agent is the superclass of the entities Person and Collective Agent Is a superclass of PERSON (entity) COLLECTIVE AGENT (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 “is. A” relationship Example: The entities Person (an individual) and Collective Agent (a group) are subclasses of the entity Agent. AGENT (entity) Is a subclass of PERSON (entity) COLLECTIVE AGENT (entity) Person “is. A” Agent Collective Agent “is. A” 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 “is. A” hierarchies, the entities in the model are disjoint. ” (IFLA LRM (2017 -12) 5. 2) ENTITY A IS DISJOINT WITH ENTITY B 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. PERSON (entity) IS DISJOINT WITH COLLECTIVE AGENT (entity) (cannot be a) These entities have an “is. A” 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 WORK (entity) IS DISJOINT WITH EXPRESSION (entity) IS DISJOINT WITH MANIFESTATION (entity) IS DISJOINT WITH ITEM (entity) 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: Category attribute: Novel Representative Expression attribute: English WORK (entity) A type of data which characterizes specific instances of an entity Relationship: BOOK (entity) WAS PUBLISHED TIME-SPAN (entity) 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-E 6 -A 1] Field of activity [LRM-E 6 -A 2] Language [LRM-E 6 -A 3] The Person entity “inherits” these attributes and adds the following attribute: ■ Profession/Occupation [LRM-E 7 -A 1] 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: Range: The source entity, or departure point, for a relationship 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) IS REALIZED THROUGH EXPRESSION (RANGE) In the inverse relationship “Expression ‘realizes’ Work, ” Expression is the domain and Work is the range. EXPRESSION (DOMAIN) REALIZES WORK (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