6.2. Data Description Section of the DRM Abstract Model (3YUK)
The Data Description section of the DRM abstract model is shown in Figure 6-2. Links between this standardization and other standardization areas are indicated by the link number that corresponds to the link number in the DRM abstract model. (3YUL)
Figure 6-2 DRM Data Description Abstract Model (3YUM)
The following are definitions for each of the concepts and relationships shown above. The following conventions are used: (3YUN)
- The concepts are presented in an order that will ensure the best possible understanding, and specific examples are provided where appropriate; (3YUO)
- Though cardinality is not expressed in the figure, the descriptions below may include cardinality (e.g. “one or more”) for purposes of clarity. Each concept will be referred to in a quantity of one (e.g. “An Entity contains an Attribute”) for purposes of simplicity. (3YUP)
- Concept names will be capitalized as in the figure itself (e.g. “Digital Data Resource”), while relationship names will be expressed in italics, and without any hyphens that may appear in the relationship name in the figure (e.g. “is constrained by”). This is done so that the definitions below can take on as narrative a tone as possible. The reader should therefore be able to easily visually navigate through the figure as they read the definitions below. (3YUQ)
- Data Schema (3YUR)
- A representation of metadata, often in the form of data artifacts such as logical data models or conceptual data models. The Data Schema concept is actually a concept group, which is an aggregation of related concepts. The Data Schema concept group is comprised of those concepts pertaining to the representation of structured data. (3YUS)
- Relationships: (3YUT)
- Entity (3YUW)
- An abstraction for a person, place, object, event, or concept described (or characterized) by common Attributes. For example, “Person” and “Agency” are Entities. An instance of an Entity represents one particular occurrence of the Entity, such as a specific person or a specific agency. (3YUX)
- Relationships: (3YUY)
- Data Type (3YW1)
- A constraint on the type of data that an instance of an Attribute may hold (e.g. "string" or "integer"). (3YV2)
- Attribute (3YV5)
- A characteristic of an Entity whose value may be used to help distinguish one instance of an Entity from other instances of the same Entity. For example, an Attribute of a “Person” Entity may be “Social Security Number (SSN)”. An SSN is used to distinguish one person (i.e. one instance of a “Person” Entity) from another. (3YV6)
- Relationships: (3YV7)
- An Attribute is constrained by a Data Type Example: The “SSN” Attribute of a “Person” Entity may have a Data Type of “string” (if hyphens are included with the SSN) or “integer” (if hyphens are not included). Relationship: Describes the relationship between two Entities. (3YV8)
- Relatonships: (3YW3)
- Digital Data Resource (3YVC)
- A digital container of information, typically known as a file. A Digital Data Resource may be one of three specific types of data resources, each corresponding to one of the three types of data described earlier, and each described below (see “Structured Data Resource”, “Semi-Structured Data Resource”, and “Unstructured Data Resource”). (3YVD)
- Relationships: (3YVE)
- Semi-Structured Data Resource (3YVL)
- A Digital Data Resource containing semi-structured data. (3YVM)
- Relationships: (3YVV)
NOTE: While a Document can contain structured data, it normally has explanatory material included, which would cause it to therefore be considered semi-structured. It is for this reason that there is no “contains” relationship from Document to Structured Data Resource. It is very important to separate Documents from Structured Data Resources because they are processed very differently. The difference between a Document and a Digital Data Resource, therefore, is that a Digital Data Resource can contained structured data. (3YVZ)
The table below provides attributes [25] that are associated with each concept in the Data Description section of the DRM abstract model. A description will be given for each attribute, along with an example where necessary for clarity. All Unstructured Data Resource attributes and their descriptions are taken from the Dublin Core Metadata Initiative (DCMI), Version 1.1, available at http://dublincore.org/documents/dcmi-terms/. All references to “resource” within descriptions of Unstructured Data Resource should therefore be interpreted as “Unstructured Data Resource”. The above URL provides additional information on attribute descriptions and usage. (3YW0)
-------- Concept--------Attribute------------Description-----------------------Example
(3YW5)
[24] It should be noted that the term “relationship” is used in two ways here. The concept named “Relationship” participates in relationships with other concepts in the abstract model, and also defines the relationship between entities when it is applied to a specific scenario. (3YW6)
[25] It should be noted that the term “attribute” is used here in a different way than for the concept named “Attribute”. Here, an “attribute” is used to describe characteristics of each of the concepts in the abstract model. (3YW7)
[1] or [26] The “Identifier” attribute is described at an abstract level in order to be consistent with the abstract nature of the reference model. Therefore, there are no references to aspects such as identifier uniqueness, representation format, or similar. Implementations based on the DRM will introduce such aspects as needed according to their requirements. (3YW8)
[27] As shown in the abstract model, a Digital Data Resource may be one of these three specific types of data resources. The same general idea applies to the entries for the “Semi-Structured Data Resource” and “Data Object” concepts above. (3YW9)
[29] It should be noted that the term “entity” here, and in subsequent Dublin Core attributes, does not have the same exact meaning as the “Entity” concept of the Data Description abstract model. (3YWA)