diff --git a/src/database/schema.sql b/src/database/schema.sql
index 86d3d6a..8a4281c 100644
--- a/src/database/schema.sql
+++ b/src/database/schema.sql
@@ -1,21 +1,33 @@
--- Tasks table
+-- Groups table with participant caching
+CREATE TABLE IF NOT EXISTS groups (
+  id TEXT PRIMARY KEY, -- WhatsApp group ID
+  name TEXT NOT NULL DEFAULT 'Unnamed group',
+  participants TEXT NOT NULL, -- JSON array of phone numbers
+  linked_parent TEXT, -- Parent community ID
+  last_updated TEXT -- ISO 8601 timestamp of last update
+);
+
+-- Tasks table with phone number assignments
 CREATE TABLE IF NOT EXISTS tasks (
   id INTEGER PRIMARY KEY AUTOINCREMENT,
   description TEXT NOT NULL,
-  assigned_to TEXT, -- WhatsApp user ID or phone number
+  assigned_to TEXT NOT NULL, -- WhatsApp phone number
   due_date TEXT, -- ISO 8601 date string (e.g., "2023-10-31")
-  completed BOOLEAN DEFAULT FALSE
+  completed BOOLEAN NOT NULL DEFAULT FALSE,
+  created_at TEXT NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  updated_at TEXT NOT NULL DEFAULT CURRENT_TIMESTAMP
 );
 
--- Groups table
-CREATE TABLE IF NOT EXISTS groups (
-  id TEXT PRIMARY KEY, -- WhatsApp group ID
-  name TEXT NOT NULL DEFAULT 'Unnamed group',
-  linked_parent TEXT -- Parent community ID
-);
-
--- Users table (optional, for future use)
+-- Users table for name mapping
 CREATE TABLE IF NOT EXISTS users (
-  id TEXT PRIMARY KEY, -- WhatsApp user ID or phone number
-  name TEXT NOT NULL
+  phone_number TEXT PRIMARY KEY, -- WhatsApp phone number
+  name TEXT NOT NULL,
+  last_seen TEXT -- ISO 8601 timestamp of last activity
 );
+
+-- Create triggers for task timestamps
+CREATE TRIGGER IF NOT EXISTS update_task_timestamp
+AFTER UPDATE ON tasks
+BEGIN
+  UPDATE tasks SET updated_at = CURRENT_TIMESTAMP WHERE id = NEW.id;
+END;