diff --git a/core-spec/osi-schema.json b/core-spec/osi-schema.json
index f24e45f1..96a250e8 100644
--- a/core-spec/osi-schema.json
+++ b/core-spec/osi-schema.json
@@ -124,6 +124,101 @@
       ],
       "description": "Logical data type for fields and metrics, independent of role (e.g. dimension vs fact) and physical representation. `Decimal` is exact base-10 with unspecified precision and scale; `Float` is approximate. `DateTime` has no timezone or offset, while `DateTimeTz` identifies an instant using offset or timezone context but does not guarantee preservation of a named timezone. Omit `datatype` when unknown; use `Opaque` plus `custom_extensions` for a known type outside the portable vocabulary."
     },
+    "SemanticType": {
+      "description": "High-level semantic classification of a field or metric. Either a well-known token or a URI pointing to an external type system.",
+      "oneOf": [
+        {
+          "type": "string",
+          "enum": ["categorical", "quantitative", "monetary", "temporal", "geographic", "ordinal", "identifier"],
+          "description": "Well-known semantic type token"
+        },
+        {
+          "type": "string",
+          "format": "uri",
+          "description": "URI pointing to an external type system (e.g., ISO 20022, FIBO, SKOS vocabulary)"
+        }
+      ]
+    },
+    "DesiredDirection": {
+      "type": "string",
+      "enum": ["higher_is_better", "lower_is_better", "neutral"],
+      "description": "KPI polarity indicating whether higher or lower values are preferred"
+    },
+    "DefaultAggregation": {
+      "type": "string",
+      "enum": ["sum", "avg", "min", "max", "count", "count_distinct"],
+      "description": "Default aggregation function to apply when this field is used as a measure"
+    },
+    "DefaultTimeGranularity": {
+      "type": "string",
+      "enum": ["day", "week", "month", "quarter", "year"],
+      "description": "Default time bucket for temporal fields"
+    },
+    "UnitSystem": {
+      "type": "string",
+      "enum": ["si", "imperial", "custom"],
+      "description": "Unit system classification"
+    },
+    "Measurement": {
+      "type": "object",
+      "description": "Describes what a numeric value represents (units and measurement)",
+      "properties": {
+        "quantity_kind": {
+          "type": "string",
+          "description": "The kind of quantity (e.g., currency, length, weight, temperature, percentage, duration)"
+        },
+        "unit": {
+          "type": "string",
+          "description": "Specific unit. For currency use ISO 4217 (e.g., usd, eur). For others use UCUM or descriptive strings."
+        },
+        "unit_system": {
+          "$ref": "#/$defs/UnitSystem"
+        }
+      },
+      "additionalProperties": false
+    },
+    "DefaultSort": {
+      "type": "object",
+      "description": "Default sorting behavior",
+      "properties": {
+        "direction": {
+          "type": "string",
+          "enum": ["asc", "desc"],
+          "description": "Sort direction"
+        },
+        "nulls": {
+          "type": "string",
+          "enum": ["first", "last"],
+          "description": "Null value positioning"
+        },
+        "by_field": {
+          "type": "string",
+          "description": "Sort by a different field (e.g., sort month names by month number)"
+        }
+      },
+      "additionalProperties": false
+    },
+    "SemanticMapping": {
+      "type": "object",
+      "description": "Link to an external ontology or standard using a SKOS-based predicate. The predicate vocabulary is intentionally open to allow non-positive assertions (e.g. DISTINCT_FROM) via extensions.",
+      "properties": {
+        "target": {
+          "type": "string",
+          "format": "uri",
+          "description": "URI of the external concept (e.g., https://schema.org/MonetaryAmount, https://spec.edmcouncil.org/fibo/...)"
+        },
+        "predicate": {
+          "type": "string",
+          "description": "Relationship type. SKOS baseline: exactMatch, closeMatch, broadMatch, narrowMatch, relatedMatch. Defaults to exactMatch. Vocabulary is open — non-standard predicates (e.g., DISTINCT_FROM) are permitted."
+        },
+        "provenance": {
+          "type": "string",
+          "description": "Optional: origin of this mapping (e.g., 'manual', 'FIBO 4.1', a tool name)"
+        }
+      },
+      "required": ["target"],
+      "additionalProperties": false
+    },
     "Dimension": {
       "type": "object",
       "description": "Dimension metadata",
@@ -153,6 +248,10 @@
           "type": "string",
           "description": "Label for categorization"
         },
+        "display_label": {
+          "type": "string",
+          "description": "Human-readable display name for UI and AI interaction"
+        },
         "description": {
           "type": "string",
           "description": "Human-readable description"
@@ -163,6 +262,40 @@
         "ai_context": {
           "$ref": "#/$defs/AIContext"
         },
+        "semantic_type": {
+          "$ref": "#/$defs/SemanticType"
+        },
+        "measurement": {
+          "$ref": "#/$defs/Measurement"
+        },
+        "display_format": {
+          "type": "string",
+          "description": "Excel-compatible display format string (e.g., $#,##0.00, 0.0%, #,##0)"
+        },
+        "default_aggregation": {
+          "$ref": "#/$defs/DefaultAggregation"
+        },
+        "default_sort": {
+          "$ref": "#/$defs/DefaultSort"
+        },
+        "default_time_granularity": {
+          "$ref": "#/$defs/DefaultTimeGranularity"
+        },
+        "semantic_mappings": {
+          "type": "array",
+          "items": {
+            "$ref": "#/$defs/SemanticMapping"
+          },
+          "description": "Links to external ontologies or standards"
+        },
+        "hidden": {
+          "type": "boolean",
+          "description": "Whether this field should be hidden from consumer UIs"
+        },
+        "group_label": {
+          "type": "string",
+          "description": "Organizational grouping label for UI presentation"
+        },
         "custom_extensions": {
           "type": "array",
           "items": {
@@ -291,6 +424,41 @@
         "ai_context": {
           "$ref": "#/$defs/AIContext"
         },
+        "display_label": {
+          "type": "string",
+          "description": "Human-readable display name for UI and AI interaction"
+        },
+        "semantic_type": {
+          "$ref": "#/$defs/SemanticType"
+        },
+        "measurement": {
+          "$ref": "#/$defs/Measurement"
+        },
+        "display_format": {
+          "type": "string",
+          "description": "Excel-compatible display format string (e.g., $#,##0.00, 0.0%, #,##0)"
+        },
+        "desired_direction": {
+          "$ref": "#/$defs/DesiredDirection"
+        },
+        "default_sort": {
+          "$ref": "#/$defs/DefaultSort"
+        },
+        "semantic_mappings": {
+          "type": "array",
+          "items": {
+            "$ref": "#/$defs/SemanticMapping"
+          },
+          "description": "Links to external ontologies or standards"
+        },
+        "hidden": {
+          "type": "boolean",
+          "description": "Whether this metric should be hidden from consumer UIs"
+        },
+        "group_label": {
+          "type": "string",
+          "description": "Organizational grouping label for UI presentation"
+        },
         "custom_extensions": {
           "type": "array",
           "items": {
diff --git a/core-spec/spec.md b/core-spec/spec.md
index 156cb1db..d31ef335 100644
--- a/core-spec/spec.md
+++ b/core-spec/spec.md
@@ -234,9 +234,19 @@ Fields represent row-level attributes that can be used for grouping, filtering,
 | `expression` | object | Yes | Expression definition with dialect support |
 | `dimension` | object | No | Dimension metadata (e.g., `is_time` flag) |
 | `label` | string | No | Label for categorization |
+| `display_label` | string | No | Human-readable display name for UI and AI interaction |
 | `description` | string | No | Human-readable description |
 | `datatype` | string (enum) | No | Logical data type for this field. See [Data types](#data-types). |
 | `ai_context` | string/object | No | Additional context for AI tools (e.g., synonyms) |
+| `semantic_type` | string | No | High-level semantic classification (see [Semantic Type](#semantic-type)) |
+| `measurement` | object | No | Unit and quantity metadata (see [Measurement](#measurement)) |
+| `display_format` | string | No | Excel-compatible format string (e.g., `$#,##0.00`, `0.0%`) |
+| `default_aggregation` | string | No | Default aggregation when used as a measure: `sum`, `avg`, `min`, `max`, `count`, `count_distinct` |
+| `default_sort` | object | No | Default sorting behavior (see [Default Sort](#default-sort)) |
+| `default_time_granularity` | string | No | Default time bucket for temporal fields: `day`, `week`, `month`, `quarter`, `year` |
+| `semantic_mappings` | array | No | Links to external ontologies (see [Semantic Mappings](#semantic-mappings)) |
+| `hidden` | boolean | No | Whether this field should be hidden from consumer UIs |
+| `group_label` | string | No | Organizational grouping label for UI presentation |
 | `custom_extensions` | array | No | Vendor-specific attributes |
 
 ### Expression Object
@@ -369,6 +379,15 @@ Quantitative measures defined on business data, representing key calculations li
 | `description` | string | No | Human-readable description of what the metric measures |
 | `datatype` | string (enum) | No | Logical data type for this metric. See [Data types](#data-types). |
 | `ai_context` | string/object | No | Additional context for AI tools (e.g., synonyms) |
+| `display_label` | string | No | Human-readable display name for UI and AI interaction |
+| `semantic_type` | string | No | High-level semantic classification (see [Semantic Type](#semantic-type)) |
+| `measurement` | object | No | Unit and quantity metadata (see [Measurement](#measurement)) |
+| `display_format` | string | No | Excel-compatible format string (e.g., `$#,##0.00`, `0.0%`) |
+| `desired_direction` | string | No | KPI polarity: `higher_is_better`, `lower_is_better`, `neutral` |
+| `default_sort` | object | No | Default sorting behavior (see [Default Sort](#default-sort)) |
+| `semantic_mappings` | array | No | Links to external ontologies (see [Semantic Mappings](#semantic-mappings)) |
+| `hidden` | boolean | No | Whether this metric should be hidden from consumer UIs |
+| `group_label` | string | No | Organizational grouping label for UI presentation |
 | `custom_extensions` | array | No | Vendor-specific attributes |
 
 ### Expression Object
@@ -417,6 +436,210 @@ expression:
 
 ---
 
+## Extended Metadata Types
+
+The following types are used by the extended metadata fields on both fields and metrics. All extended metadata is **optional** and **non-executional** — it does not affect query execution but enables consumers (BI tools, AI agents, developers) to correctly interpret, render, and present data.
+
+### Semantic Type
+
+High-level classification of a field or metric value. Accepts either a **well-known token** or a **URI** pointing to an external type system. Using URIs keeps the field registry-agnostic and allows governed external type systems to carry the long tail of domain-specific types.
+
+**Well-known tokens:**
+
+| Value | Description |
+|-------|-------------|
+| `categorical` | Unordered categorical values (e.g., status, color) |
+| `quantitative` | Numeric values representing quantities |
+| `monetary` | Currency/financial values |
+| `temporal` | Time or date values |
+| `geographic` | Location-related values (country, lat/lng, region) |
+| `ordinal` | Ordered categorical values (e.g., Low/Medium/High, ratings) |
+| `identifier` | Unique identifiers (e.g., IDs, codes) |
+
+**URI examples** (for regulated or domain-specific types):
+
+```yaml
+semantic_type: https://www.iso20022.org/glossary/LEI
+semantic_type: https://fpml.org/types/ISIN
+semantic_type: https://spec.edmcouncil.org/fibo/ontology/FBC/ProductsAndServices/FinancialProductsAndServices/UPI
+```
+
+### Measurement
+
+Describes what a numeric value represents. Enables unit-aware reasoning and formatting.
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `quantity_kind` | string | The kind of quantity (e.g., `currency`, `length`, `weight`, `temperature`, `percentage`, `duration`) |
+| `unit` | string | Specific unit. For currency, use ISO 4217 codes (e.g., `usd`, `eur`, `gbp`). For others, use UCUM or descriptive strings (e.g., `meters`, `kg`, `celsius`) |
+| `unit_system` | string | Unit system: `si`, `imperial`, `custom` |
+
+**Example:**
+
+```yaml
+measurement:
+  quantity_kind: currency
+  unit: usd
+  unit_system: custom
+```
+
+### Default Sort
+
+Defines default sorting behavior for a field or metric.
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `direction` | string | Sort direction: `asc`, `desc` |
+| `nulls` | string | Null positioning: `first`, `last` |
+| `by_field` | string | Sort by a different field (e.g., sort month names by month number) |
+
+**Example:**
+
+```yaml
+default_sort:
+  direction: desc
+  nulls: last
+```
+
+### Semantic Mappings
+
+Links a field or metric to external ontologies or standards using a SKOS-based predicate. The predicate vocabulary is **intentionally open** — the SKOS predicates provide a well-understood baseline, but non-standard predicates (e.g., `DISTINCT_FROM` for regulatory disambiguation) are permitted and can be expressed via extensions without being schema-invalid.
+
+| Field | Type | Required | Description |
+|-------|------|----------|-------------|
+| `target` | string (URI) | Yes | URI of the external concept |
+| `predicate` | string | No | Relationship type. Defaults to `exactMatch`. SKOS baseline predicates listed below. Vocabulary is open. |
+| `provenance` | string | No | Origin of this mapping (e.g., `"manual"`, `"FIBO 4.1"`, a tool name) |
+
+**SKOS baseline predicates:**
+
+| Predicate | Meaning |
+|-----------|--------|
+| `exactMatch` | Concepts are sufficiently similar to be used interchangeably (default) |
+| `closeMatch` | Concepts are similar enough to be useful in some contexts |
+| `broadMatch` | Target concept is broader (more general) |
+| `narrowMatch` | Target concept is narrower (more specific) |
+| `relatedMatch` | Concepts are associatively related |
+
+**Example — standard alignment:**
+
+```yaml
+semantic_mappings:
+  - target: https://schema.org/MonetaryAmount
+    predicate: exactMatch
+    provenance: manual
+```
+
+**Example — regulatory disambiguation (open predicate):**
+
+```yaml
+semantic_mappings:
+  - target: https://spec.edmcouncil.org/fibo/ontology/DER/RateDerivatives/IRSwaps/Counterparty
+    predicate: exactMatch
+    provenance: FIBO 4.1
+  - target: https://www.esma.europa.eu/emir/Counterparty
+    predicate: DISTINCT_FROM
+    provenance: EMIR-vs-MiFIR mapping review 2024
+```
+
+### Display Format
+
+The `display_format` string follows Excel-compatible custom number format conventions. Consumers MAY support a subset, but interoperability is improved when adhering to common patterns.
+
+**Common Patterns:**
+
+| Pattern | Description | Example Output |
+|---------|-------------|----------------|
+| `$#,##0.00` | Currency with 2 decimals | $1,234.56 |
+| `#,##0` | Integer with grouping | 12,345 |
+| `0.0%` | Percentage with 1 decimal | 12.3% |
+| `#,##0.00;(#,##0.00)` | Positive/negative | 1,234.56 or (1,234.56) |
+| `0.00E+00` | Scientific notation | 1.23E+04 |
+| `yyyy-mm-dd` | Date format | 2024-01-15 |
+
+---
+
+## Extended Metadata Examples
+
+**Field with full extended metadata:**
+
+```yaml
+- name: sales_amount
+  expression:
+    dialects:
+      - dialect: ANSI_SQL
+        expression: sales_amount
+  display_label: "Sales Amount"
+  semantic_type: monetary
+  measurement:
+    quantity_kind: currency
+    unit: usd
+  display_format: "$#,##0.00"
+  default_aggregation: sum
+  default_sort:
+    direction: desc
+    nulls: last
+  semantic_mappings:
+    - target: https://schema.org/MonetaryAmount
+      predicate: exactMatch
+  group_label: "Revenue"
+```
+
+**Metric with extended metadata:**
+
+```yaml
+- name: total_sales
+  expression:
+    dialects:
+      - dialect: ANSI_SQL
+        expression: SUM(orders.sales_amount)
+  display_label: "Total Sales"
+  description: Total revenue from all completed orders
+  semantic_type: monetary
+  measurement:
+    quantity_kind: currency
+    unit: usd
+  display_format: "$#,##0.00"
+  desired_direction: higher_is_better
+  default_sort:
+    direction: desc
+  group_label: "Revenue"
+  semantic_mappings:
+    - target: https://schema.org/MonetaryAmount
+      predicate: exactMatch
+```
+
+**Temporal field with time granularity:**
+
+```yaml
+- name: order_date
+  expression:
+    dialects:
+      - dialect: ANSI_SQL
+        expression: order_date
+  dimension:
+    is_time: true
+  display_label: "Order Date"
+  semantic_type: temporal
+  default_time_granularity: month
+  default_sort:
+    direction: desc
+```
+
+**Hidden field used only in expressions:**
+
+```yaml
+- name: internal_cost_basis
+  expression:
+    dialects:
+      - dialect: ANSI_SQL
+        expression: raw_cost * adjustment_factor
+  hidden: true
+  description: Internal cost calculation used by margin metrics
+```
+
+---
+
 ## Custom Extensions
 
 Custom extensions allow vendors to add platform-specific metadata without breaking core compatibility. Each extension includes a vendor name and arbitrary JSON data.
diff --git a/core-spec/spec.yaml b/core-spec/spec.yaml
index 32fbb3e1..8f19c574 100644
--- a/core-spec/spec.yaml
+++ b/core-spec/spec.yaml
@@ -211,6 +211,10 @@ fields:
     # Optional: Label for categorization (e.g., "filter")
     label: string
 
+    # Optional: Human-readable display name for UI and AI interaction
+    # Provides a user-friendly name distinct from the technical field name
+    display_label: string
+
     # Optional: Human-readable description of the field
     description: string
 
@@ -226,6 +230,71 @@ fields:
     # Helps LLMs understand the field meaning and generate better queries
     ai_context: string
 
+    # Optional: High-level semantic classification of the field
+    # Helps consumers determine appropriate visualization and handling
+    # Either a well-known token OR a URI pointing to an external type system
+    # Well-known tokens: categorical, quantitative, monetary, temporal, geographic, ordinal, identifier
+    # URI examples: https://www.iso20022.org/glossary/LEI, https://fpml.org/types/ISIN
+    semantic_type: string
+
+    # Optional: Describes what a numeric value represents (units and measurement)
+    # Enables unit-aware reasoning and formatting
+    measurement:
+      # Optional: The kind of quantity being measured
+      # Examples: currency, length, weight, temperature, percentage, duration
+      quantity_kind: string
+      # Optional: The specific unit of measurement
+      # For currency, use ISO 4217 codes (e.g., usd, eur, gbp)
+      # For other units, use UCUM or descriptive strings (e.g., meters, kg, celsius)
+      unit: string
+      # Optional: The unit system
+      # Values: si, imperial, custom
+      unit_system: string
+
+    # Optional: Display format string for presentation
+    # Uses Excel-compatible custom number format conventions
+    # Examples: "$#,##0.00", "0.0%", "#,##0", "yyyy-mm-dd"
+    # Consumers MAY fall back to default formatting if unsupported
+    display_format: string
+
+    # Optional: Default aggregation behavior when this field is used as a measure
+    # Removes ambiguity in query generation for consumers
+    # Values: sum, avg, min, max, count, count_distinct
+    default_aggregation: string
+
+    # Optional: Default sorting behavior for this field
+    default_sort:
+      # Optional: Sort direction
+      # Values: asc, desc
+      direction: string
+      # Optional: Null handling
+      # Values: first, last
+      nulls: string
+      # Optional: Sort by a different field (e.g., sort month names by month number)
+      by_field: string
+
+    # Optional: Default time granularity for temporal fields
+    # Only applicable when dimension.is_time is true
+    # Values: day, week, month, quarter, year
+    default_time_granularity: string
+
+    # Optional: Links to external ontologies or standards
+    # Uses SKOS-based predicates as a baseline but the predicate vocabulary is open,
+    # allowing extensions to express non-positive assertions (e.g., DISTINCT_FROM)
+    semantic_mappings:
+      - target: string      # URI of the external concept (e.g., https://schema.org/MonetaryAmount)
+        predicate: string   # Relationship type. SKOS baseline: exactMatch, closeMatch, broadMatch,
+                            # narrowMatch, relatedMatch. Defaults to exactMatch. Vocabulary is open.
+        provenance: string  # Optional: source of this mapping (e.g., "manual", "FIBO 4.1", a tool name)
+
+    # Optional: Whether this field should be hidden from consumer UIs
+    # Hidden fields remain available for expressions but are not surfaced to end users
+    hidden: boolean
+
+    # Optional: Organizational grouping label for UI presentation
+    # Used to organize fields into logical folders or categories
+    group_label: string
+
     # Optional: Vendor-specific attributes for extensibility
     custom_extensions:
       - vendor_name: string  # Free-form string identifying the vendor
@@ -263,6 +332,46 @@ metrics:
     # Helps LLMs understand the metric meaning and suggest it appropriately
     ai_context: string
 
+    # Optional: Human-readable display name for UI and AI interaction
+    display_label: string
+
+    # Optional: High-level semantic classification of the metric
+    # Either a well-known token OR a URI pointing to an external type system
+    # Well-known tokens: categorical, quantitative, monetary, temporal, geographic, ordinal, identifier
+    semantic_type: string
+
+    # Optional: Describes what the metric value represents (units and measurement)
+    measurement:
+      quantity_kind: string
+      unit: string
+      unit_system: string
+
+    # Optional: Display format string for presentation
+    # Uses Excel-compatible custom number format conventions
+    display_format: string
+
+    # Optional: Indicates KPI polarity for scorecards and AI summarization
+    # Values: higher_is_better, lower_is_better, neutral
+    desired_direction: string
+
+    # Optional: Default sorting behavior for this metric
+    default_sort:
+      direction: string  # asc, desc
+      nulls: string      # first, last
+
+    # Optional: Links to external ontologies or standards
+    # Uses SKOS-based predicates as a baseline but the predicate vocabulary is open
+    semantic_mappings:
+      - target: string      # URI of the external concept
+        predicate: string   # Relationship type (SKOS baseline, open vocabulary). Default: exactMatch
+        provenance: string  # Optional: source of this mapping
+
+    # Optional: Whether this metric should be hidden from consumer UIs
+    hidden: boolean
+
+    # Optional: Organizational grouping label for UI presentation
+    group_label: string
+
     # Optional: Vendor-specific attributes for extensibility
     custom_extensions:
       - vendor_name: string  # Free-form string identifying the vendor