Structured data 2 (#645)

* Structured data refactor - multi-index tables, remove need for manual mods to the Cassandra tables

* Tech spec updated to track implementation

trustgraph-base/trustgraph/schema/services/rows_query.py

@@ -0,0 +1,32 @@
+from dataclasses import dataclass, field
+from typing import Optional
+
+from ..core.primitives import Error
+from ..core.topic import topic
+
+############################################################################
+
+# Rows Query Service - executes GraphQL queries against structured data
+
+@dataclass
+class GraphQLError:
+    message: str = ""
+    path: list[str] = field(default_factory=list)       # Path to the field that caused the error
+    extensions: dict[str, str] = field(default_factory=dict)   # Additional error metadata
+
+@dataclass
+class RowsQueryRequest:
+    user: str = ""              # Cassandra keyspace (follows pattern from TriplesQueryRequest)
+    collection: str = ""        # Data collection identifier (required for partition key)
+    query: str = ""             # GraphQL query string
+    variables: dict[str, str] = field(default_factory=dict)    # GraphQL variables
+    operation_name: Optional[str] = None    # Operation to execute for multi-operation documents
+
+@dataclass
+class RowsQueryResponse:
+    error: Error | None = None              # System-level error (connection, timeout, etc.)
+    data: str = ""              # JSON-encoded GraphQL response data
+    errors: list[GraphQLError] = field(default_factory=list) # GraphQL field-level errors
+    extensions: dict[str, str] = field(default_factory=dict)   # Query metadata (execution time, etc.)
+
+############################################################################