1. Documenting, Maintaining, and Sharing
Documenting, Maintaining, and Sharing
Standard Variables with DDI Version 3.0:
the ISCO example
Joachim Wackerow
GESIS-ZUMA
German Social Science Infrastructure Services /
Centre for Survey Research and Methodology
IASSIST 2007, May 16
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2. Outline ISCO ISCO in DDI 3 DDI 3 as Metadata Repository Description
Revisions / Versions
ISCO in DDI 3
Variable Description
Comparison of Variables
Standalone Resource Package
DDI 3 as Metadata Repository

3. Intention of presentation
Intention of presentation
ISCO as an example to show reuse of metadata by the means of DDI 3.0
Not a presentation on the content of the ISCO classification
Focus on documenting standard variables in standalone resources
Report on first experiences with DDI 3.0 -
ISCO is just used as an example to show some features of the new DDI
Similar to the previous presentation it is an report on first experiences with the new DDI
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4. ISCO Description International Standard Classification of Occupations
ISCO Description
International Standard Classification of Occupations
Maintained by the International Labour Organization (ILO)
ISCO is a tool for organizing jobs into a clearly defined set of groups according to the tasks and duties undertaken in the job.
ISCO organizes occupations in a hierarchical framework. At the lowest level is the unit of classification - a job - which is defined as a set of tasks or duties designed to be executed by one person.
Jobs are grouped into occupations according to the degree of similarity in their constituent tasks and duties.
ISCO is defined in four levels of aggregation, for example ISCO-88(COM) consists of:
10 major groups
28 sub-major groups (subdivisions of major groups)
116 minor groups (subdivisions of sub-major groups)
390 unit groups (subdivisions of minor groups)
Description citation from ILO
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5. ISCO Example: Major Group 6 Skilled agricultural and fishery workers
ISCO Example: Major Group 6 Skilled agricultural and fishery workers
61 Skilled agricultural and fishery workers
611 Market gardeners and crop growers
6111 Field crop and vegetable growers
6112 Gardeners, horticultural and nursery growers
612 Animal producers and related workers
6121 Dairy and livestock producers
6122 Poultry producers
6129 Animal producers and related workers not elsewhere classified
613 Crop and animal producers
6130 Crop and animal producers
Clipping of major group 6
Here only one category exists on the sub-major group level. This is the same as on the major group level.
Minor group with two unit groups.
Two other minor groups.
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6. Revisions / Versions of ISCO
1958, 1968, 1988 (current revision), 2008 (draft)
Versions with minor differences exist, for example:
ISCO-88(COM) for the European Union (Eurostat)
ISCO-88(CIS) for the Commonwealth of Independent States (CIS Statistical Committee)
ISCO-88(OCWM) Occupational Classification of Workers in Migration under ISCO-88 of ILO/UNDP Asian Regional Programme on International Labour Migration (ILO, Bangkok, 1992)
Country-specific variants
Country-specific classifications which can be converted into ISCO

7. Examples for ISCO usage in major studies
Examples for ISCO usage in major studies
Direct usage
ESS - European Social Survey
ISSP - International Social Survey Programme
The Eurobarometer Survey Series
SOEP – German Socio-Economic Panel Study
Conversion from other occupation classification
GSS (US General Social Survey) - ISCO-68, converted from 1970 U.S. Census Classification of Occupations and Industries
German Microcensus – ISCO-88(COM), converted from classification KldB92
German panel study from the presentation before uses the Eurpean Union variant of ISCO-88
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8. Standard Variables
ISCO as a standard variable facilitates the usage of an occupation variable in multiple studies
Comparison of studies is one of the major goals of standard variables
By using standard variables within an organization or across a group of organizations central documentation and maintenance of these variables is improved
Standard variables can be maintained in a variable repository
The variable repository should be processable by applications for better exploitation
DDI 3 provides the metadata structure for a machine-actionable variable repository

9. DDI: Metadata Structure for Variable Repositories
DDI: Metadata Structure for Variable Repositories
Different parts of a variable are documented in different schemes. This enables reuse of these parts.
Central description of a variable in a variable scheme
Variable scheme
ISCO-88(COM)
… other variables
Category codes are listed in a code scheme which can be referenced by a one or more variables
Example: Occupation of respondent, occupation of spouse of respondent
Schemes are basically a list of items
“variable explosion”, term from Wendy Thomas, sounds like demolition, but it is really the reverse -
Description of categories: labels, missing categories
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10. DDI: ISCO Hierarchy of Codes Example: Major Group 6
61 Skilled agricultural and fishery workers
611 Market gardeners and crop growers
6111 Field crop and vegetable growers
6112 Gardeners, horticultural and nursery growers
612 Animal producers and related workers
6121 Dairy and livestock producers
6122 Poultry producers
6129 Animal producers and related workers not elsewhere classified
613 Crop and animal producers
6130 Crop and animal producers

11. DDI: ISCO Hierarchy of Codes Example: Major Group 6
DDI: ISCO Hierarchy of Codes Example: Major Group 6 61
611
6111
6112
612
6121
6122
6129
613
6130
This forms a regular hierarchy. All codes on a lower level form one code of a higher level. Achieved by nesting.
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12. DDI: Metadata Structure for Variable Repositories
DDI: Metadata Structure for Variable Repositories
Different parts of a variable are documented in different schemes. This enables reuse of these parts.
Central description of variable in a variable scheme
Codes for categories are listed in a code scheme which can be referenced by a one or more variables
Description of categories in a category scheme which can be referenced by one or more code schemes
Schemes are basically a list of items
“variable explosion”, term from Wendy Thomas, sounds like demolition, but it is really the reverse -
Description of categories: labels, missing categories
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13. DDI: ISCO Hierarchy of Codes Example: Major Group 6
61 Skilled agricultural and fishery workers
611 Market gardeners and crop growers
6111 Field crop and vegetable growers
6112 Gardeners, horticultural and nursery growers
612 Animal producers and related workers
6121 Dairy and livestock producers
6122 Poultry producers
6129 Animal producers and related workers not elsewhere classified
613 Crop and animal producers
6130 Crop and animal producers

14. DDI: ISCO Hierarchy of Codes Example: Major Group 6
Skilled agricultural and fishery workers
Market gardeners and crop growers
Field crop and vegetable growers
Gardeners, horticultural and nursery growers
Animal producers and related workers
Dairy and livestock producers
Poultry producers
Animal producers and related workers not elsewhere classified
Crop and animal producers

15. DDI: Metadata Structure for Variable Repositories
DDI: Metadata Structure for Variable Repositories
Different parts of a variable are documented in different schemes. This enables reuse of these parts.
Central description of variable in a variable scheme
Codes for categories are listed in a code scheme which can be referenced by a one or more variables
Description of categories in a category scheme which can be referenced by one or more code schemes
Multiple languages can be used in the documentation, important for labels
Schemes are basically a list of items
“variable explosion”, term from Wendy Thomas, sounds like demolition, but it is really the reverse -
Description of categories: labels, missing categories in a list
Additional language would not result in a new variable, it would be documented parallet to the first language.
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16. DDI: Category Example Multiple Languages
<l:Category>
<r:Identification>
<r:ID>Level2Category61</r:ID>
</r:Identification>
<r:Label xml:lang ="en">Skilled agricultural and
fishery workers</r:Label>
<r:Label xml:lang="de">Fachkräfte in der
Landwirtschaft und Fischerei</r:Label>
<r:Label xml:lang ="fr">Agriculteurs et ouvriers
qualifiés de l'agriculture et de la pêche</r:Label>
</l:Category>

17.
DDI: Concepts
A variable represents a theoretical concept about the reality, for ISCO the concept is “Work”.
Concepts are described in DDI 3 in a concept scheme. Similar variables can point to the same concept.
Additionally the concepts can be organized in concept groups. The concept for ISCO is more precisely “Paid work”. “Work” is the more general concept which can comprehend other types of work.
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18. DDI: Minor changes of variables New revisions of variables
DDI: Minor changes of variables New revisions of variables
Variables, code and category schemes undergo changes, i.e. error correction. This change can be documented in a new version of the same DDI scheme.
The responsible agency can be documented. Both version and maintaining agency are part of the global unique identifier of an item
urn:ddi:3_0:CodeScheme:gesis.org:lp:2_0.ISCO88:1_0
Additional documentation: version date, version responsibility, version rationale
Scheme or item like category
If an application doesn’t use a specific version, the version with the highest number will be used.
Example of minor change: different wording of a label
Category would get new a new version number and also the containing category scheme.
URN - Uniform Resource Name
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19. DDI: Minor changes of variables New revisions of variables
DDI: Minor changes of variables New revisions of variables
Variables, code and category schemes undergo changes, i.e. error correction. This change can be documented in a new version of the same DDI scheme.
For ISCO a new revision is published every 10 years. Different versions exist for example for ISCO-88. Most of these versions are still used.
So they can be documented in DDI as separate variables, not as separate versions.
If an application doesn’t use a specific version, the version with the highest number will be used.
Example of minor change: different wording of a label
Category would get new a new version number and also the containing category scheme.
URN - Uniform Resource Name
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20. DDI: Relationship between Similar Variables
DDI: Relationship between Similar Variables
The relationship between these similar variables can be documented in comparison tables
ISCO-88 ISCO-08 Category
Tree and shrub crop growers
Mixed crop growers
Derived categories can be described in the category scheme
6123 and 6124 (ISCO-88) to
6124 (ISCO-08) Apiarists and sericulturists
Human-readable description
Derivation command of the used program / package
The type of relationship on code or category level can be expressed.
A machine-actionable description of the comparison quality seems to be missing.
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21. DDI: Resource Package Resource Package … Concept „Paid Work“
Concept Group „Work“
Comparison Table Codes
Ref. to
ISCO-88
Ref. to 6114
ISCO-08
Ref. to 6115
Variable Scheme
Variable „ISCO-68“
Variable „ISCO-88“
Code 6114
Code Scheme „ISCO-88“ …
Category „Mixed crop grwr”
Category Scheme „ISCO-88“ …

22. DDI: Resource Package as Reusable Set of Metadata
DDI: Resource Package as Reusable Set of Metadata
Resource packages can be used by multiple studies documented in DDI.
The same metadata is reused and this implies potential comparability
European Social Survey
Variable Reference
Resource Package
Concept „Work“
Code Scheme „ISCO-88“
Variable „ISCO-88 “
Category Scheme „ISCO-88“
Eurobarometer
Variable Reference
Items in local or remote resource packages can be referenced by an global unique identifier.
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23. DDI: Resource Package as Reusable Set of Metadata
DDI: Resource Package as Reusable Set of Metadata
Schemes in resource packages can be used in multiple ways.
Study
Variable
„Occupation of Spouse“
Resource Package
Concept „Work“
Code Scheme „ISCO-88“
Variable „ISCO-88 “
Category Scheme „ISCO-88“
Variable
„Occupation of Father“
Items in local or remote resource packages can be referenced by an global unique identifier.
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24. DDI: Resource Package Metadata Repository
DDI: Resource Package Metadata Repository
Concepts, variables, code schemes, and category schemes as a whole create a metadata registry
DDI 3 borrowed ideas from the standard ISO/IEC (description of the structure for metadata registries on an abstract level)
A metadata registry (for offline or online usage) requires an application in addition to the metadata structure
Full advantage of a metadata registry by a search front end and by web services for programs
Variable search by web page.
Integration of reusable metadata in other application.
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25. DDI and ISO/IEC 11179 Data Element Value Domain Permissible Value
DDI and ISO/IEC 11179
Data Element
Value Domain
Permissible Value
Diagram thanks to Chris Nelson.
This core part of DDI maps directly to equivalent constructs in ISO/IEC
In ISO/IEC different terms are used.
Data Element
Concept
Conceptual Domain
Value Meaning
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26. Conclusion Advantages in usage of DDI metadata repositories
Conclusion
Advantages in usage of DDI metadata repositories
Easy exchange of the documentation of standard variables
Enabling metadata mining for finding potential comparable studies
Support for survey designers, when questionnaires are included
Can support the process of establishing a standard variable
Basis of metadata registry application
Requirements / Limitations
Requires often a well established standard variable like ISCO
Acting in a controlled environment is required, quality assurance
Trusted relationship to maintaining organization is necessary, especially when using automated access like a web service
Large variety of “standard variables” for one concept can cause problems
Using DDI 3 resource packages is one step into the direction of “Building global knowledge communities with open metadata”
Advantages
Support for survey designers, when metadata repositories are expanded by the related questionnaires
Requirements / Limitatations (more general)
Controled way can be an advantage within an organization
local modifications are often made to improve the accuracy of a measured subject, but at the same time the standardization and the implied comparison potential can loose on quality
Machine-actionable qualifier for comparison required
Final remark
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27. Thank you for your attention
Basic DDI example on ISCO-88(COM) available at DDI 3.0 page:
African Scops Owl