1.
Establishing Schema Definitions within the
Self-Sovereign Identity (SSI) Ecosystem
Paul Knowles
- Innovation & Emerging Technology, Dativa
- Chair of the Schemas and Overlays WG, Sovrin Foundation
Overlays 1O1:
SSIMeetup.orghttps://creativecommons.org/licenses/by-sa/4.0/
Robert Mitwicki
- Co-Founder & Software Engineering, Lab10 Collective
- Member of the Schemas and Overlays WG, Sovrin Foundation

2.
1. Empower global SSI communities
2. Open to everyone interested in SSI
3. All content is shared with CC BY SA
SSIMeetup.org
Alex Preukschat @SSIMeetup @AlexPreukschat
Coordinating Node SSIMeetup.org
https://creativecommons.org/licenses/by-sa/4.0/
SSIMeetup objectives

3.
What is a Schema?
Schema. A machine-readable definition of the semantics of a data structure.
Schemas are used to define the Attributes used in one or more Credential
Definitions.
- Sovrin Glossary (version 2)
SSIMeetup.orghttps://creativecommons.org/licenses/by-sa/4.0/

4.
What is an Overlay?
Overlay. A data structure that provides an extra layer of contextual and/or
conditional information to a Schema. This extra context can be used by an
Agent to transform how information is displayed to a viewer or to guide the
Agent in how to apply a custom process to Schema data.
- Sovrin Glossary (version 2)
SSIMeetup.orghttps://creativecommons.org/licenses/by-sa/4.0/

5.
Why are Overlays useful?
• Overlays allow an Agent to add extra layers of conditional or contextual
information to a Schema;
• Overlays allow an Agent to update contextual information without having to
reissue a new Schema;
• Overlays ensure that Schema can remain generic thus allowing diverse use
cases per Schema;
• Overlays ensure that Schema definitions can remain in their simplest form
thus providing a standard base from which to decentralise data;
• The Overlay design has very little impact on the existing Hyperledger Indy*
solution. * Although early phase development will take place on Hyperledger
Indy, the aim is to develop the code to be platform agnostic.
SSIMeetup.orghttps://creativecommons.org/licenses/by-sa/4.0/

6.
Initial Implementation
International non-profit global
public utility for self-sovereign
identity
Open source code for SSI
contributed by Sovrin to
Linux Foundation
SSIMeetup.orghttps://creativecommons.org/licenses/by-sa/4.0/

7.
Types of Overlay
• Entry Overlay -> to add predefined field values to Schema attributes;
• Conditional Overlay -> to add conditional programming to a Schema;
• Label Overlay -> to add category and attribute labels to Schema attributes
(incl. language translations);
• Informational Overlay -> to add descriptions and contextual information to a
Schema (incl. service hints and informational text);
• Sensitive Overlay (Holder only) -> to enable a Holder to flag user-defined
sensitive attributes;
• Subset Overlay -> to create a Schema subset
SSIMeetup.orghttps://creativecommons.org/licenses/by-sa/4.0/

8.
Deficiencies from a tech implementation perspective
GDPR :
• Introducing the …
Blinding Identity Taxonomy (BIT)
• The need for a common standard to help protect the
privacy of personally identifiable information (PII) about
people, organizations, or things
SSIMeetup.orghttps://creativecommons.org/licenses/by-sa/4.0/

9.
• Names (incl. First Names, Last Names, Full Names, Entity Names)
• Physical Addresses
• E-mail Addresses
• Telephone Numbers
• Postal Codes
• Personal Software Application Handles (e.g. Skype, Slack, Hyperledger
Chat, etc.)
• Profile Pages
• Passport Numbers
• Social Security Numbers
• National Insurance Numbers
• Driving License Numbers
• Vehicle Registration Numbers
• Bank Account Numbers
• Credit (or Debit) Card Numbers
• Personal Identification Numbers (PIN)
• Self-sovereign Key Identifiers
• Decentralised Identifiers (DIDs)
• Employee Identifiers
• Account Identifiers
• Governmental Identifiers
• Membership Identifiers (e.g. Trade Union Membership, etc.)
• Institutional Identifiers (e.g. Private Health Care Identifiers, etc.)
• Case Identifiers (e.g. Case ID Numbers, Benefit Plan Participation
Identifiers, etc.)
• User Identifiers (e.g. User IDs, Logins, etc.)
• Passwords
• Signatures
• Digital Certificates
• Photos
• Videos
• Images
• Vocal Sound Bites
• Dates (e.g. Date of Birth, etc.)*
• Genetic Identifiers (incl. chromosomal, deoxyribonucleic acid
(DNA) and ribonucleic acid (RNA) data)
• Biometric Identifiers (incl. voiceprints, iris scans, facial imaging
and dactyloscopic (fingerprint) data)
• Internet Protocol (IP) Addresses
• Media Access Control (MAC) Addresses
• GPS Locational Information
• Cookie Browser Identifiers
• Radio Frequency Identifiers
• IoT Identifiers (incl. smart meter data)
• International Mobile Equipment Identity (IMEI)
• International Mobile Subscriber Identity (IMSI)
• Social media interactive elements, posts and comments (incl.
likes, emojis and polling results)
• Free-Form Text Fields / Unstructured Data**
Blinding Identity Taxonomy(BIT)
https://creativecommons.org/licenses/by-sa/4.0/
* Not all captured dates will reveal identity but some will so, if in doubt, encrypt.
** Defn.: Text which does not have a given structure, nor which is entered in
any specific format. Note: All free-form text fields should be encrypted.

10.
BIT Schema Object
• To flag personally identifiable information (PII) attributes that could unblind the
identity of a person, an organization or a thing with reference to the Blinding
Identity Taxonomy (BIT).
SSIMeetup.orghttps://creativecommons.org/licenses/by-sa/4.0/

11.
Creating a Schema with
linked Overlays
SSIMeetup.orghttps://creativecommons.org/licenses/by-sa/4.0/

12.
{
"attributes": {
"birthDate": "Date",
"age": "Integer",
"ageUnit": "String",
"gender": "String",
"ethnicGroup": "String",
"race1": "TrueClass",
"race2": "TrueClass",
"race2Specific": "String",
"race3": "TrueClass",
"race4": "TrueClass",
"race5": "TrueClass",
"race6": "TrueClass"
},
"bit_attributes": [
{
"birthDate": "sensitive"
}
],
"did": "did:sov:3214abcd",
"name": "Demographics",
"description": "Created by MEDIDATA",
"version": "1.0",
"formSource": "DEM"
}
“Demographics”
Schema
Schema metadata
attributenames&
types
BIT Schema Object :
The Schema attribute “birthDate” has been
flagged by the Issuer as “Dates (e.g. Date of
Birth, etc.)” is one of the 44 listed elements
in the Blinding Identity Taxonomy (BIT)
Schema
SSIMeetup.orghttps://creativecommons.org/licenses/by-sa/4.0/

13.
Entry Overlay
{
"did": "did:sov:1234abcd",
"type": "spec/overlay/1.0/entry",
"name": "Demographics Entry",
"schemaDID": "did:sov:3214abcd",
"schemaVersion": "1.0",
"schemaName": "Demographics",
"predefined_values": {
"ageUnit": [
"YEAR"
],
"gender": [
"MALE",
"FEMALE"
],
"ethnicGroup": [
"HISPANIC OR LATINO",
"NOT HISPANIC OR LATINO",
"NOT REPORTED",
"UNKNOWN"
],
"race2Specific": [
"CHINESE",
"TAIWANESE",
"ASIAN INDIAN",
"KOREAN",
"MALAYSIAN",
"VIETNAMESE",
"OTHER ASIAN"
]
}
}
ENTRY_OVERLAY
Overlay metadata
predefinedfield
values
Schema reference

14.
Conditional Overlay
{
"did": "did:sov:9837hdv74ef",
"type": "spec/overlay/1.0/conditional",
"name": "Demographics Conditional",
"schemaDID": "did:sov:3214abcd",
"schemaVersion": "1.0",
"schemaName": "Demographics",
"conditional": {
"hidden_attributes": [
{
"race2Specific": ":race2 == false"
}
],
"required_attributes": [
{
"birthDate": true,
"gender": true,
"ageUnit": ":age != null"
}
]
}
}
CONDITIONAL_OVERLAY
Overlay metadata
conditional
programming
Schema reference
SSIMeetup.orghttps://creativecommons.org/licenses/by-sa/4.0/

15.
Label Overlay
{
"did": "did:sov:59248239",
"type": "spec/overlay/1.0/label",
"name": "Demographics Label English",
"schemaDID": "did:sov:3214abcd",
"schemaVersion": "1.0",
"schemaName": "Demographics",
"language": "en_US",
"attribute_labels": {
"birthDate": "Date of Birth",
"age": "Age",
"ageUnit": "Age unit",
"gender": "Sex",
"ethnicGroup": "Ethnicity",
"race1": "American Indian or Alaska Native",
"race2": "Asian",
"race2Specific": "If race is Asian, specify origin",
"race3": "Black or African American",
"race4": "Native Hawaiian or Other Pacific Islander",
"race5": "White",
“race6": "Race Unknown"
},
"attribute_categories": {
"race": [
"race1",
"race2",
"race2Specific",
"race3",
“race4",
"race5",
"race6"
]
},
"category_labels": {
"race": "Race"
}
}
LABEL_OVERLAY
Schema reference
Overlay metadata
attribute
labels
definingand
labelling
categories
Language definition
SSIMeetup.orghttps://creativecommons.org/licenses/by-sa/4.0/

16.
Informational Overlay
{
"did": "did:sov:58kosf0239",
"type": "spec/overlay/1.0/informational",
"name": "Demographics Informational",
"schemaDID": "did:sov:3214abcd",
"schemaVersion": "1.0",
"schemaName": "Demographics",
"language": "en_US",
"attribute_instructions": {
"birthDate": "Fill in your Date of Birth",
"age": "Fill in your Age",
"gender": "Choose your Sex",
"ethnicGroup": "Choose your Ethnicity",
"race1": "Select if you are American Indian or Alaska Native",
"race2": "Select if you are Asian",
"race2Specific": "If race is Asian, select Specific Origin",
"race3": "Select if you are Black or African American",
"race4": "Select if you are Native Hawaiian or Other Pacific Islander",
“race5": "Select if you are White",
"race6": "Select if if race is Unknown"
},
"category_instructions": {
"race": "Select all that apply"
}
}
INFORMATIONAL_OVERLAY
Overlay metadata
informational
text
Schema reference

17.
Sensitive Overlay
(Holder only)
{
"did": "did:sov:12idksjabcd",
"type": "spec/overlay/1.0/sensitive",
"name": “Sensitive",
"attributes": [
"gender"
]
}
SENSITIVE_OVERLAY
Overlay metadata
user-defined
sensitive attributes
No Schema reference
SSIMeetup.orghttps://creativecommons.org/licenses/by-sa/4.0/

18.
Subset Overlay
{
"did": "did:sov:1123414abcd",
"type": "spec/overlay/1.0/subset",
"name": "Demographics Subset",
"schemaDID": "did:sov:3214abcd",
"schemaVersion": "1.0",
"schemaName": "Demographics",
"attributes": [
"birthDate",
"age",
"ageUnit",
"gender"
]
}
SUBSET_OVERLAY
Overlay metadata
defining attributes for a
schema subset
Schema reference
SSIMeetup.orghttps://creativecommons.org/licenses/by-sa/4.0/

19.
Overlays: Demo
Robert Mitwicki
- Co-Founder & Software Engineering, Lab10 Collective
- Member of the Schemas and Overlays WG, Sovrin Foundation
SSIMeetup.orghttps://creativecommons.org/licenses/by-sa/4.0/

20.
Establishing Schema Definitions within the
Self-Sovereign Identity (SSI) Ecosystem
Paul Knowles
- Innovation & Emerging Technology, Dativa
- Chair of the Schemas and Overlays WG, Sovrin Foundation
Overlays 1O1:
SSIMeetup.orghttps://creativecommons.org/licenses/by-sa/4.0/
Robert Mitwicki
- Co-Founder & Software Engineering, Lab10 Collective
- Member of the Schemas and Overlays WG, Sovrin Foundation