DDI 3'0

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DDI 3.0

• Conceptual Model Chris Nelson

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Why Have a Model

• Non syntactic representation of the business
  domain
• Useful for identifying common constructs
• Identification, versioning etc.
• patterns
• A good basis for designing syntactic
  representation (e.g. XML) schemas, databases, and
  processing systems
• Industry tools support this process (e.g. EMF)

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DDI 2.0
Archive
Study Unit

• Driven by the need to archive data
• Developed as an XML DTD
• No formal conceptual model
• No re-use of artifacts

Variable Scheme
Category Scheme
Questions
Physical Data Product
Physical Instance
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DDI 3.0 design goals life-cycle model
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DDI 2.0
Archive
Study Unit
Variable Scheme
Category Scheme
Questions
Physical Data Product
Physical Instance
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DDI 3.0
Group
Archive
Study Unit
Data/Metadata Management
Variable Scheme
Physical Data Product
Category Scheme
Concept Scheme
Data Metadata Structure
Question Bank
Instrument
Structural Metadata
NCube Record Layout
Metadata Report
Physical Instance
Data/Metadata Resource
Identification, Item Schemes, Item Scheme
Associations Component Schemes, Organisations
DDI Base
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DDI 3.0
Group
Archive
Study Unit
Data/Metadata Management
Variable Scheme
Physical Data Product
Category Scheme
Concept Scheme
Data Metadata Structure
Question Bank
Instrument
NCube TableLayout
Structural Metadata
NCubeLayout
NCube Record Layout
In Line NCube Record Layout
Metadata Report
Physical Instance
Data/Metadata Resource
Identification, Item Schemes, Item Scheme
Associations Component Schemes, Organisations
DDI Base
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Instrumentation module

• Important metadata is entered at this stage and
  should be carried forward to the end data
  product.
• Information about question flow, cues presented
  to the respondents etc. is important for the
  interpretation of the data
• Often complex relationships between questions and
  variables.

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UML Constructs as used in the DDI Conceptual Model
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Classes and Associations (1)
cardinalities
0.. 0..1 1.. 1
zero or more zero or one one or more one
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Classes and Associations (2)- Aggregates
CategoryItem is subordinate to and belongs to
CategoryScheme
In the model diagrams in this presentation there
is no distinction made between aggregate by
reference and aggregate by value. All aggregates
are shown with a open diamond.
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Classes and Associations (3)- Unidirectional
Variable is navigable from DataAttribute but not
vice-versa
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Sub Classes - Inheritance
DimensionVariable inherits from Variable (i.e. it
is a specialisation of Variable). Therefore
DimensionVariable can have an association to
MetadataReport. However, any associations from
DimensionVariable are specific to
DimensionaVariable and are not applicable to
Variable
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Abstract Classes
An abstract class is drawn because it is a useful
way of grouping classes, and avoids drawing a
complex diagram with lots of association lines,
but where it is not foreseen that the class
serves any other purpose (i.e. it is always
implemented as one of its sub classes). Here
Instrument inherits the attributes of Id, uri,
urn.
Instrument can have a multilingual name and
description.
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Instrument - Simplified Class Diagram
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Question Bank - Simplified Class Diagram
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Variable - Simplified Class Diagram
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Identifying potentially comparative data

• The grouping mechanism can be used to mark up
  families of studies that from the outset have
  been designed to be comparable.
• ...or families of studies that has been made
  comparable through a harmonization process.
• However, none of these mechanisms reach beyond
  the limit of the DDI 3.0-wrapper that binds the
  family of studies together.
• One of the biggest challenges for DDI 3.0 has
  been to define a way to describe relationships
  between variables across DDI-wrappers,
  collections and servers.
• Use-case Give me more variables like this, in
  other words the ability to identify potentially
  comparative variables across studies,
  collections, archives and locations.

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Identifying potentially comparative data

• There is a mechanism in the existing DDI that to
  a certain degree will allow you do this. That is
  the ability to assign concepts from external
  vocabularies to variables.

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Identifying potentially comparative data

• In DDI 3.0 there will a more elaborated solution
  to the same problem, a specification of an
  external registry-like question-bank or
  classification database that will allow you to
  register concepts, questions and variables.
• The specification can be used to set up local
  question banks or question banks that are global
  to many organizations.
• The specification will also support statements
  about differences between registered variables

External registry

• The registry can be seen as an extension to a
  standard DDI document.
• ...but the specification might also include the
  interfaces to allow this to be set up and run as
  a proper registry on the Web.

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Registries

• Contains metadata that allows users/ applications
  to find things
• The objects themselves do not need to be in the
  registry
• But must be accessible over the internet
  (preferably accessible by standardised queries
  and retrievable in a standardised format)
• E.g. questions in question bank category
  schemes variables
• Registries can have repositories to store local
  content
• Registry standards exist and registry products
  are available
• But they need to be customised to support the
  domain(e.g. customised software that understands
  the DDI model and syntax implementation)
• If objects can be identified in a globally unique
  way, then they can be accessed and shared

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Data Analysis
Data Metadata Structure
Physical Data Product
NCube Record Layout
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Cube Structure - Simplified
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Data Structure
NCube Logical Product
NCube Record Layout
Physical Instance
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Cube Data Contains or Points to Data
Link to the Cube Structure Definition
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DDI 3.0 Metadata

• Metadata constructs that are fairly generic and
  can be attached at various places in the
  hierarchy.
• Examples
• Coding instructions
• Description of time and geography
• Citation/Abstract
• Methodology etc.
• The DDI model contains a metamodel for metadata
  structures
• Identifies the object types to which metadata can
  be attached
• Specifies the category/concept schemes that
  contains the list of valid identifiers for the
  object types
• Specifies the metadata reports that can be made
  (e. g. coding instructions, citation) in terms of
• Attributes
• Value domain (e.g. format) of the attributes
• Reporting hierarchy of the attribute
• Identifies to which object types the metadata
  report can be associated

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Metadata Structure Definition
uses defined concepts
concept defined in
Metadata Report
Concept Scheme
Concept
takes semantic and context from
Format and Permitted Value List
Value domain
can have hierarchy
specifies to which object types the report can be
attached
Object Identifier
defines the object types to which metadata can be
attached
identifies target object type of the identifier
Specifies components for each Object (key
identifies the value domain of the component
identifies target object type of the component
Target Object Type
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Metadata Structure
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Metadata Set Contains Metadata Reports
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Modularity and grouping as a way to handle
comparative data
Group
Study design
Ques- tions
Variab- les
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Modularity and grouping as a way to handle
multiple tables/cubes
Group
Study description
Variables
Category Schemes
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Group Logical Combination of Artifacts
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Thank You