Hippo Configuration Reference¶

Complete reference for configuring Hippo, the Metadata Tracking Service (MTS) for the BASS platform.

Overview¶

Hippo uses two primary configuration files:

config.json -- Main application configuration that specifies the schema path and storage settings
Schema files (YAML or JSON) -- Define entity types, attributes, validators, and inheritance in LinkML format

Configuration is loaded via load_hippo_config() from config.json, and schemas are loaded via SchemaParser or load_schema().

HippoConfig¶

The main configuration model for the Hippo application. Loaded from config.json.

Field	Type	Default	Description
`schema_path`	`Path`	(required)	Path to the schema directory or file containing entity definitions
`storage_backend`	`str`	`None`	Storage backend to use (e.g., `"sqlite"`, `"postgresql"`). If `None`, uses default backend
`database_url`	`str`	`None`	Connection string for the database. For SQLite: `hippo.db` or absolute path
`validation_enabled`	`bool`	`true`	Enable validation of entity data against schema rules
`validation_fail_fast`	`bool`	`true`	Stop validation on first error. If `false`, collects all validation errors
`write_path_validation_enabled`	`bool`	`true`	Enable validation of write paths (entity location paths)
`write_path_validation_timeout`	`float`	`None`	Timeout in seconds for write path validation. `None` = no timeout
`validators_path`	`Path`	`None`	Path to custom validators file. If `None`, uses default location

schema_path is required -- HippoConfig will not instantiate without it.

Example config.json¶

{
  "schema_path": "./schemas",
  "storage_backend": "sqlite",
  "database_url": "./data/hippo.db",
  "validation_enabled": true,
  "validation_fail_fast": true,
  "write_path_validation_enabled": true,
  "validators_path": "./validators.yaml"
}

Template config.json (from `hippo init`)¶

The basic template generated by hippo init produces:

{
  "version": "0.1",
  "storage": {
    "type": "sqlite",
    "path": "hippo.db"
  },
  "schema": {
    "type": "linkml"
  }
}

The full template includes additional sections:

{
  "version": "0.1",
  "name": "hippo-project",
  "description": "Hippo Metadata Tracking Service Project",
  "storage": {
    "type": "sqlite",
    "path": "hippo.db"
  },
  "schema": {
    "type": "linkml",
    "path": "schemas"
  },
  "validation": {
    "enabled": true,
    "strict": false
  },
  "api": {
    "host": "127.0.0.1",
    "port": 8000
  }
}

LinkML Schema Format¶

Schema files use standard LinkML format. Classes and their attributes are defined in a dictionary structure with a required schema header. Both YAML and JSON are accepted.

Schema Header¶

Every LinkML schema file requires these top-level keys:

Key	Required	Description
`id`	Yes	Unique URI identifier for the schema
`name`	Yes	Short schema name (alphanumeric, underscores, dashes)
`prefixes`	Yes	Maps prefix names to IRI namespaces (must include `linkml`)
`imports`	Yes	List of imported schemas (almost always includes `linkml:types`)
`default_range`	Recommended	Default data type for attributes without explicit range (e.g., `string`)
`classes`	Core	Dictionary of class (entity type) definitions
`enums`	Core	Dictionary of enumeration definitions
`slots`	Optional	Dictionary of reusable slot definitions shared across classes

Schema Example¶

id: https://example.org/my-lab
name: my_lab
prefixes:
  linkml: https://w3id.org/linkml/
  my_lab: https://example.org/my-lab/
imports:
  - linkml:types
default_range: string

enums:
  SexType:
    permissible_values:
      M:
      F:
      Unknown:

  SampleType:
    permissible_values:
      tissue:
      blood:
      csf:

classes:
  Donor:
    description: "Human donor information"
    attributes:
      donor_id:
        range: string
        required: true
        identifier: true
        annotations:
          hippo_index: true
      species:
        range: string
        required: true
        ifabsent: "string(Homo sapiens)"
      sex:
        range: SexType
        required: true
      date_of_birth:
        range: date
      consent_obtained:
        range: boolean
        ifabsent: "false"

  Sample:
    description: "Biological sample from a donor"
    attributes:
      sample_id:
        range: string
        required: true
        identifier: true
        annotations:
          hippo_index: true
      donor:
        range: Donor
        required: true
        annotations:
          hippo_index: true
      sample_type:
        range: SampleType
        required: true
      quantity_ng:
        range: float
      notes:
        range: string
        annotations:
          hippo_search: fts5

Schema Inheritance¶

Schemas support inheritance via is_a:

classes:
  BiologicalEntity:
    description: "Base entity for all biological samples"
    abstract: true
    attributes:
      external_id:
        range: string
        identifier: true

  Donor:
    is_a: BiologicalEntity
    description: "Human donor information"
    attributes:
      donor_id:
        range: string
        required: true
      species:
        range: string

Mixins are supported for composing shared attribute sets:

classes:
  BrainEntity:
    mixin: true
    attributes:
      brain_region:
        range: string

  BrainSample:
    is_a: Sample
    mixins:
      - BrainEntity

Attribute Properties¶

Each attribute within a class supports these LinkML properties:

Property	Type	Default	Description
`range`	`str`	schema's `default_range`	Data type: a built-in type, class name, or enum name
`required`	`bool`	`false`	Whether the attribute is required (non-null)
`description`	`str`	`None`	Human-readable description
`ifabsent`	`str`	`None`	Default value expression, e.g., `string(pending)`, `int(0)`, `true`
`identifier`	`bool`	`false`	Whether this attribute is the unique primary key
`multivalued`	`bool`	`false`	Whether the value is a list
`pattern`	`str`	`None`	Regex pattern for validation
`minimum_value`	`number`	`None`	Minimum numeric value (inclusive)
`maximum_value`	`number`	`None`	Maximum numeric value (inclusive)
`inlined`	`bool`	`false`	Whether class-range values are nested inline
`inlined_as_list`	`bool`	`false`	Inlined as a list rather than a dictionary

Built-in Range Types¶

Available when you import linkml:types:

Range	Description
`string`	Text data
`integer`	Integer numbers
`float`	Floating-point numbers
`boolean`	True/false values
`date`	Date (YYYY-MM-DD)
`datetime`	Date and time (ISO 8601)
`uri`	URI/URL string
`uriorcurie`	URI or compact URI (CURIE)

Hippo-Specific Annotations¶

Hippo extends standard LinkML with storage annotations. These are expressed under the annotations key on attributes:

Annotation	Values	Description
`hippo_index`	`true`	Creates a B-tree database index on this attribute
`hippo_index_partial`	`true`	Creates a partial index (non-null values only)
`hippo_search`	`fts`, `fts5`, `embedding`	Enables full-text search indexing

  diagnosis:
    range: string
    annotations:
      hippo_index: true
      hippo_search: fts5

References (Entity Links)¶

Declare that an attribute points to another class by setting range to a class name:

classes:
  Sample:
    attributes:
      donor:
        range: Donor          # references the Donor class
        required: true

When the range is a class, Hippo treats the attribute as an entity reference. This is used for HippoClient.schema_references() and Cappella's collection resolver.

Enum Definitions¶

Enums are defined at the schema top level under enums:. Each enum declares its allowed values under permissible_values:

enums:
  SexType:
    description: "Biological sex"
    permissible_values:
      M:
        description: "Male"
      F:
        description: "Female"
      Unknown:
        description: "Not specified"

Reference an enum from an attribute with range:

  sex:
    range: SexType
    required: true

ValidatorDefinition¶

Defines a validator applied to entity data. Validators are loaded from a separate validators file with the CEL (Common Expression Language) engine:

validators:
  - name: sample_name_required
    type: cel
    enabled: true
    priority: 0
    config:
      entity_types: [Sample]
      on: [create, update]
      condition: 'entity.name != ""'
      error: "Sample {entity_id}: name is required"

Field	Type	Default	Description
`name`	`str`	(required)	Unique name for this validator
`type`	`str`	(required)	Validator type (e.g., `"cel"` for CEL expressions)
`enabled`	`bool`	`true`	Whether this validator is active
`priority`	`int`	`0`	Execution order (higher runs first). Negative for pre-schema validation
`config`	`dict[str, Any]`	`None`	Type-specific configuration

Complete Example¶

config.json¶

{
  "schema_path": "./schemas",
  "storage_backend": "sqlite",
  "database_url": "./data/hippo.db",
  "validation_enabled": true,
  "validation_fail_fast": false,
  "write_path_validation_enabled": true,
  "validators_path": "./validators.yaml"
}

schemas/base.yaml -- Base Entity¶

id: https://example.org/base
name: base
prefixes:
  linkml: https://w3id.org/linkml/
  base: https://example.org/base/
imports:
  - linkml:types
default_range: string

classes:
  BiologicalEntity:
    description: "Base entity for all biological samples"
    abstract: true
    attributes:
      external_id:
        range: string
        identifier: true
        description: "External system identifier"
      created_by:
        range: string
        description: "User who created this entity"

schemas/donor.yaml -- Donor Entity¶

id: https://example.org/donor
name: donor
prefixes:
  linkml: https://w3id.org/linkml/
  donor: https://example.org/donor/
imports:
  - linkml:types
  - base
default_range: string

enums:
  SexType:
    permissible_values:
      M:
      F:
      Unknown:

classes:
  Donor:
    is_a: BiologicalEntity
    description: "Human donor information"
    attributes:
      donor_id:
        range: string
        required: true
        identifier: true
        annotations:
          hippo_index: true
        description: "Internal donor identifier"
      species:
        range: string
        required: true
        ifabsent: "string(Homo sapiens)"
        description: "Species of the donor"
      sex:
        range: SexType
        required: true
        description: "Biological sex"
      date_of_birth:
        range: date
        description: "Date of birth"
      ethnicity:
        range: string
        description: "Ethnicity information"
      consent_obtained:
        range: boolean
        ifabsent: "false"
        description: "Whether donor consent is on file"
      consent_date:
        range: date
        description: "Date consent was obtained"
      diagnoses:
        range: string
        multivalued: true
        description: "List of diagnoses"
      medical_record_number:
        range: string
        annotations:
          hippo_index: true
        description: "Hospital MRN"
      notes:
        range: string
        annotations:
          hippo_search: fts5
        description: "Free-text notes for searching"

schemas/sample.yaml -- Sample Entity¶

id: https://example.org/sample
name: sample
prefixes:
  linkml: https://w3id.org/linkml/
  sample: https://example.org/sample/
imports:
  - linkml:types
  - base
  - donor
default_range: string

enums:
  SampleType:
    permissible_values:
      tissue:
      blood:
      csf:
      cell_line:

classes:
  Sample:
    is_a: BiologicalEntity
    description: "Biological sample from a donor"
    attributes:
      sample_id:
        range: string
        required: true
        identifier: true
        annotations:
          hippo_index: true
        description: "Internal sample identifier"
      donor:
        range: Donor
        required: true
        annotations:
          hippo_index: true
        description: "Reference to donor"
      sample_type:
        range: SampleType
        required: true
        description: "Type of biological sample"
      tissue_type:
        range: string
        description: "Tissue of origin"
      collection_date:
        range: datetime
        description: "Date/time of sample collection"
      quantity_ng:
        range: float
        description: "Sample quantity in nanograms"
      quality_score:
        range: float
        description: "Sample quality metric (0-1)"
      storage_location:
        range: string
        description: "Physical storage location"
      barcode:
        range: string
        annotations:
          hippo_index: true
        description: "Sample barcode"
    unique_keys:
      barcode_key:
        unique_key_slots:
          - barcode

validators.yaml¶

validators:
  - name: donor_id_format
    entity_types: [Donor]
    'on': [create, update]
    condition: 'entity.donor_id.matches("^DON-\\d{6}$")'
    error: "Donor {entity_id}: donor_id must match format DON-123456"

  - name: sample_quantity_positive
    entity_types: [Sample]
    'on': [create, update]
    condition: 'entity.quantity_ng > 0'
    error: "Sample {entity_id}: quantity_ng must be positive"

  - name: sample_with_donor
    entity_types: [Sample]
    'on': [create]
    condition: 'entity.donor != ""'
    error: "Sample {entity_id}: must have an associated donor"

Loading Configuration¶

from hippo.config.loader import load_hippo_config, load_schema

# Load main configuration
config = load_hippo_config("config.json")

# Load a schema file
schema = load_schema("schemas/donor.yaml")

# Load all schemas from a directory
from hippo.config.loader import SchemaParser
parser = SchemaParser(schema_dir=Path("schemas"))
schemas = parser.load_schema_dir(Path("schemas"))