diff --git a/CHANGELOG.md b/CHANGELOG.md
index 698e43b..076d3fd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,20 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- Added `format` and `platform` fields to packages table (#16)
+- Added `checksum_md5` and `metadata` JSONB fields to artifacts table (#16)
+- Added `updated_at` field to tags table (#16)
+- Added `tag_name`, `user_agent`, `duration_ms`, `deduplicated`, `checksum_verified` fields to uploads table (#16)
+- Added `change_type` field to tag_history table (#16)
+- Added composite indexes for common query patterns (#16)
+- Added GIN indexes on JSONB fields for efficient JSON queries (#16)
+- Added partial index for public projects (#16)
+- Added database triggers for `updated_at` timestamps (#16)
+- Added database triggers for maintaining artifact `ref_count` accuracy (#16)
+- Added CHECK constraints for data integrity (`size > 0`, `ref_count >= 0`) (#16)
+- Added migration script `002_schema_enhancements.sql` for existing databases (#16)
+
 ## [0.1.0] - 2025-12-12
 ### Changed
 - Changed the Dockerfile npm build arg to use the deps.global.bsf.tools URL as the default registry (#45)
diff --git a/backend/app/models.py b/backend/app/models.py
index 7e1a08a..1e1256f 100644
--- a/backend/app/models.py
+++ b/backend/app/models.py
@@ -73,11 +73,12 @@ class Artifact(Base):
     size = Column(BigInteger, nullable=False)
     content_type = Column(String(255))
     original_name = Column(String(1024))
+    checksum_md5 = Column(String(32))  # MD5 hash for additional verification
+    metadata = Column(JSON, default=dict)  # Format-specific metadata
     created_at = Column(DateTime(timezone=True), default=datetime.utcnow)
     created_by = Column(String(255), nullable=False)
     ref_count = Column(Integer, default=1)
     s3_key = Column(String(1024), nullable=False)
-    format_metadata = Column(JSON, default=dict)  # Format-specific metadata (version, etc.)
 
     tags = relationship("Tag", back_populates="artifact")
     uploads = relationship("Upload", back_populates="artifact")
@@ -99,6 +100,7 @@ class Tag(Base):
     name = Column(String(255), nullable=False)
     artifact_id = Column(String(64), ForeignKey("artifacts.id"), nullable=False)
     created_at = Column(DateTime(timezone=True), default=datetime.utcnow)
+    updated_at = Column(DateTime(timezone=True), default=datetime.utcnow, onupdate=datetime.utcnow)
     created_by = Column(String(255), nullable=False)
 
     package = relationship("Package", back_populates="tags")
@@ -120,6 +122,7 @@ class TagHistory(Base):
     tag_id = Column(UUID(as_uuid=True), ForeignKey("tags.id", ondelete="CASCADE"), nullable=False)
     old_artifact_id = Column(String(64), ForeignKey("artifacts.id"))
     new_artifact_id = Column(String(64), ForeignKey("artifacts.id"), nullable=False)
+    change_type = Column(String(20), nullable=False, default="update")
     changed_at = Column(DateTime(timezone=True), default=datetime.utcnow)
     changed_by = Column(String(255), nullable=False)
 
@@ -127,6 +130,8 @@ class TagHistory(Base):
 
     __table_args__ = (
         Index("idx_tag_history_tag_id", "tag_id"),
+        Index("idx_tag_history_changed_at", "changed_at"),
+        CheckConstraint("change_type IN ('create', 'update', 'delete')", name="check_change_type"),
     )
 
 
@@ -137,6 +142,11 @@ class Upload(Base):
     artifact_id = Column(String(64), ForeignKey("artifacts.id"), nullable=False)
     package_id = Column(UUID(as_uuid=True), ForeignKey("packages.id"), nullable=False)
     original_name = Column(String(1024))
+    tag_name = Column(String(255))  # Tag assigned during upload
+    user_agent = Column(String(512))  # Client identification
+    duration_ms = Column(Integer)  # Upload timing in milliseconds
+    deduplicated = Column(Boolean, default=False)  # Whether artifact was deduplicated
+    checksum_verified = Column(Boolean, default=True)  # Whether checksum was verified
     uploaded_at = Column(DateTime(timezone=True), default=datetime.utcnow)
     uploaded_by = Column(String(255), nullable=False)
     source_ip = Column(String(45))
@@ -148,6 +158,8 @@ class Upload(Base):
         Index("idx_uploads_artifact_id", "artifact_id"),
         Index("idx_uploads_package_id", "package_id"),
         Index("idx_uploads_uploaded_at", "uploaded_at"),
+        Index("idx_uploads_package_uploaded_at", "package_id", "uploaded_at"),
+        Index("idx_uploads_uploaded_by_at", "uploaded_by", "uploaded_at"),
     )
 
 
@@ -220,4 +232,6 @@ class AuditLog(Base):
         Index("idx_audit_logs_resource", "resource"),
         Index("idx_audit_logs_user_id", "user_id"),
         Index("idx_audit_logs_timestamp", "timestamp"),
+        Index("idx_audit_logs_resource_timestamp", "resource", "timestamp"),
+        Index("idx_audit_logs_user_timestamp", "user_id", "timestamp"),
     )
diff --git a/migrations/001_initial.sql b/migrations/001_initial.sql
index 9f31947..983b96e 100644
--- a/migrations/001_initial.sql
+++ b/migrations/001_initial.sql
@@ -14,6 +14,7 @@ CREATE TABLE IF NOT EXISTS projects (
 
 CREATE INDEX idx_projects_name ON projects(name);
 CREATE INDEX idx_projects_created_by ON projects(created_by);
+CREATE INDEX idx_projects_public ON projects(name) WHERE is_public = true;
 
 -- Packages (collections within projects)
 CREATE TABLE IF NOT EXISTS packages (
@@ -21,6 +22,8 @@ CREATE TABLE IF NOT EXISTS packages (
     project_id UUID NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
     name VARCHAR(255) NOT NULL,
     description TEXT,
+    format VARCHAR(50) DEFAULT 'generic',  -- package type: generic, npm, pypi, docker, etc.
+    platform VARCHAR(50) DEFAULT 'any',    -- target platform: any, linux, darwin, windows, etc.
     created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
     updated_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
     UNIQUE(project_id, name)
@@ -28,21 +31,26 @@ CREATE TABLE IF NOT EXISTS packages (
 
 CREATE INDEX idx_packages_project_id ON packages(project_id);
 CREATE INDEX idx_packages_name ON packages(name);
+CREATE INDEX idx_packages_format ON packages(format);
+CREATE INDEX idx_packages_platform ON packages(platform);
 
 -- Artifacts (Content-Addressable)
 CREATE TABLE IF NOT EXISTS artifacts (
     id VARCHAR(64) PRIMARY KEY,  -- SHA256 hash
-    size BIGINT NOT NULL,
+    size BIGINT NOT NULL CHECK (size > 0),
     content_type VARCHAR(255),
     original_name VARCHAR(1024),
+    checksum_md5 VARCHAR(32),    -- MD5 hash for additional verification
+    metadata JSONB,              -- format-specific metadata
     created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
     created_by VARCHAR(255) NOT NULL,
-    ref_count INTEGER DEFAULT 1,
+    ref_count INTEGER DEFAULT 1 CHECK (ref_count >= 0),
     s3_key VARCHAR(1024) NOT NULL
 );
 
 CREATE INDEX idx_artifacts_created_at ON artifacts(created_at);
 CREATE INDEX idx_artifacts_created_by ON artifacts(created_by);
+CREATE INDEX idx_artifacts_metadata ON artifacts USING GIN (metadata);
 
 -- Tags (Aliases pointing to artifacts)
 CREATE TABLE IF NOT EXISTS tags (
@@ -51,12 +59,14 @@ CREATE TABLE IF NOT EXISTS tags (
     name VARCHAR(255) NOT NULL,
     artifact_id VARCHAR(64) NOT NULL REFERENCES artifacts(id),
     created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
+    updated_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
     created_by VARCHAR(255) NOT NULL,
     UNIQUE(package_id, name)
 );
 
 CREATE INDEX idx_tags_package_id ON tags(package_id);
 CREATE INDEX idx_tags_artifact_id ON tags(artifact_id);
+CREATE INDEX idx_tags_package_created_at ON tags(package_id, created_at DESC);
 
 -- Tag History (for rollback capability)
 CREATE TABLE IF NOT EXISTS tag_history (
@@ -64,11 +74,13 @@ CREATE TABLE IF NOT EXISTS tag_history (
     tag_id UUID NOT NULL REFERENCES tags(id) ON DELETE CASCADE,
     old_artifact_id VARCHAR(64) REFERENCES artifacts(id),
     new_artifact_id VARCHAR(64) NOT NULL REFERENCES artifacts(id),
+    change_type VARCHAR(20) NOT NULL DEFAULT 'update' CHECK (change_type IN ('create', 'update', 'delete')),
     changed_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
     changed_by VARCHAR(255) NOT NULL
 );
 
 CREATE INDEX idx_tag_history_tag_id ON tag_history(tag_id);
+CREATE INDEX idx_tag_history_changed_at ON tag_history(changed_at);
 
 -- Uploads (upload event records)
 CREATE TABLE IF NOT EXISTS uploads (
@@ -76,6 +88,11 @@ CREATE TABLE IF NOT EXISTS uploads (
     artifact_id VARCHAR(64) NOT NULL REFERENCES artifacts(id),
     package_id UUID NOT NULL REFERENCES packages(id),
     original_name VARCHAR(1024),
+    tag_name VARCHAR(255),              -- tag assigned during upload
+    user_agent VARCHAR(512),            -- client identification
+    duration_ms INTEGER,                -- upload timing in milliseconds
+    deduplicated BOOLEAN DEFAULT false, -- whether artifact was deduplicated
+    checksum_verified BOOLEAN DEFAULT true, -- whether checksum was verified
     uploaded_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
     uploaded_by VARCHAR(255) NOT NULL,
     source_ip VARCHAR(45)
@@ -84,6 +101,8 @@ CREATE TABLE IF NOT EXISTS uploads (
 CREATE INDEX idx_uploads_artifact_id ON uploads(artifact_id);
 CREATE INDEX idx_uploads_package_id ON uploads(package_id);
 CREATE INDEX idx_uploads_uploaded_at ON uploads(uploaded_at);
+CREATE INDEX idx_uploads_package_uploaded_at ON uploads(package_id, uploaded_at DESC);
+CREATE INDEX idx_uploads_uploaded_by_at ON uploads(uploaded_by, uploaded_at DESC);
 
 -- Consumers (Dependency tracking)
 CREATE TABLE IF NOT EXISTS consumers (
@@ -141,14 +160,17 @@ CREATE INDEX idx_audit_logs_action ON audit_logs(action);
 CREATE INDEX idx_audit_logs_resource ON audit_logs(resource);
 CREATE INDEX idx_audit_logs_user_id ON audit_logs(user_id);
 CREATE INDEX idx_audit_logs_timestamp ON audit_logs(timestamp);
+CREATE INDEX idx_audit_logs_resource_timestamp ON audit_logs(resource, timestamp DESC);
+CREATE INDEX idx_audit_logs_user_timestamp ON audit_logs(user_id, timestamp DESC);
+CREATE INDEX idx_audit_logs_details ON audit_logs USING GIN (details);
 
 -- Trigger to update tag history on changes
 CREATE OR REPLACE FUNCTION track_tag_changes()
 RETURNS TRIGGER AS $$
 BEGIN
     IF TG_OP = 'UPDATE' AND OLD.artifact_id != NEW.artifact_id THEN
-        INSERT INTO tag_history (id, tag_id, old_artifact_id, new_artifact_id, changed_at, changed_by)
-        VALUES (gen_random_uuid(), NEW.id, OLD.artifact_id, NEW.artifact_id, NOW(), NEW.created_by);
+        INSERT INTO tag_history (id, tag_id, old_artifact_id, new_artifact_id, change_type, changed_at, changed_by)
+        VALUES (gen_random_uuid(), NEW.id, OLD.artifact_id, NEW.artifact_id, 'update', NOW(), NEW.created_by);
     END IF;
     RETURN NEW;
 END;
@@ -158,3 +180,72 @@ CREATE TRIGGER tag_changes_trigger
     AFTER UPDATE ON tags
     FOR EACH ROW
     EXECUTE FUNCTION track_tag_changes();
+
+-- Trigger to auto-update updated_at timestamps
+CREATE OR REPLACE FUNCTION update_updated_at_column()
+RETURNS TRIGGER AS $$
+BEGIN
+    NEW.updated_at = NOW();
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE TRIGGER projects_updated_at_trigger
+    BEFORE UPDATE ON projects
+    FOR EACH ROW
+    EXECUTE FUNCTION update_updated_at_column();
+
+CREATE TRIGGER packages_updated_at_trigger
+    BEFORE UPDATE ON packages
+    FOR EACH ROW
+    EXECUTE FUNCTION update_updated_at_column();
+
+CREATE TRIGGER tags_updated_at_trigger
+    BEFORE UPDATE ON tags
+    FOR EACH ROW
+    EXECUTE FUNCTION update_updated_at_column();
+
+-- Triggers for maintaining artifact ref_count accuracy
+CREATE OR REPLACE FUNCTION increment_artifact_ref_count()
+RETURNS TRIGGER AS $$
+BEGIN
+    UPDATE artifacts SET ref_count = ref_count + 1 WHERE id = NEW.artifact_id;
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE OR REPLACE FUNCTION decrement_artifact_ref_count()
+RETURNS TRIGGER AS $$
+BEGIN
+    UPDATE artifacts SET ref_count = ref_count - 1 WHERE id = OLD.artifact_id;
+    RETURN OLD;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE OR REPLACE FUNCTION update_artifact_ref_count()
+RETURNS TRIGGER AS $$
+BEGIN
+    IF OLD.artifact_id != NEW.artifact_id THEN
+        UPDATE artifacts SET ref_count = ref_count - 1 WHERE id = OLD.artifact_id;
+        UPDATE artifacts SET ref_count = ref_count + 1 WHERE id = NEW.artifact_id;
+    END IF;
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+-- Note: ref_count triggers on tags table
+-- These track how many tags reference each artifact
+CREATE TRIGGER tags_ref_count_insert_trigger
+    AFTER INSERT ON tags
+    FOR EACH ROW
+    EXECUTE FUNCTION increment_artifact_ref_count();
+
+CREATE TRIGGER tags_ref_count_delete_trigger
+    AFTER DELETE ON tags
+    FOR EACH ROW
+    EXECUTE FUNCTION decrement_artifact_ref_count();
+
+CREATE TRIGGER tags_ref_count_update_trigger
+    AFTER UPDATE ON tags
+    FOR EACH ROW
+    EXECUTE FUNCTION update_artifact_ref_count();
diff --git a/migrations/002_schema_enhancements.sql b/migrations/002_schema_enhancements.sql
new file mode 100644
index 0000000..c32b13b
--- /dev/null
+++ b/migrations/002_schema_enhancements.sql
@@ -0,0 +1,170 @@
+-- Migration 002: Schema Enhancements
+-- Adds new fields, indexes, and triggers for improved functionality
+
+-- ============================================
+-- Packages: Add format and platform fields
+-- ============================================
+ALTER TABLE packages ADD COLUMN IF NOT EXISTS format VARCHAR(50) DEFAULT 'generic';
+ALTER TABLE packages ADD COLUMN IF NOT EXISTS platform VARCHAR(50) DEFAULT 'any';
+
+CREATE INDEX IF NOT EXISTS idx_packages_format ON packages(format);
+CREATE INDEX IF NOT EXISTS idx_packages_platform ON packages(platform);
+
+-- ============================================
+-- Artifacts: Add checksum_md5, metadata, and CHECK constraints
+-- ============================================
+ALTER TABLE artifacts ADD COLUMN IF NOT EXISTS checksum_md5 VARCHAR(32);
+ALTER TABLE artifacts ADD COLUMN IF NOT EXISTS metadata JSONB;
+
+-- Add CHECK constraints (will fail if data violates them)
+DO $$
+BEGIN
+    IF NOT EXISTS (SELECT 1 FROM pg_constraint WHERE conname = 'artifacts_ref_count_check') THEN
+        ALTER TABLE artifacts ADD CONSTRAINT artifacts_ref_count_check CHECK (ref_count >= 0);
+    END IF;
+    IF NOT EXISTS (SELECT 1 FROM pg_constraint WHERE conname = 'artifacts_size_check') THEN
+        ALTER TABLE artifacts ADD CONSTRAINT artifacts_size_check CHECK (size > 0);
+    END IF;
+END $$;
+
+CREATE INDEX IF NOT EXISTS idx_artifacts_metadata ON artifacts USING GIN (metadata);
+
+-- ============================================
+-- Tags: Add updated_at and composite index
+-- ============================================
+ALTER TABLE tags ADD COLUMN IF NOT EXISTS updated_at TIMESTAMP WITH TIME ZONE DEFAULT NOW();
+
+CREATE INDEX IF NOT EXISTS idx_tags_package_created_at ON tags(package_id, created_at DESC);
+
+-- ============================================
+-- Tag History: Add change_type and index
+-- ============================================
+ALTER TABLE tag_history ADD COLUMN IF NOT EXISTS change_type VARCHAR(20) DEFAULT 'update';
+
+DO $$
+BEGIN
+    IF NOT EXISTS (SELECT 1 FROM pg_constraint WHERE conname = 'tag_history_change_type_check') THEN
+        ALTER TABLE tag_history ADD CONSTRAINT tag_history_change_type_check
+            CHECK (change_type IN ('create', 'update', 'delete'));
+    END IF;
+END $$;
+
+CREATE INDEX IF NOT EXISTS idx_tag_history_changed_at ON tag_history(changed_at);
+
+-- ============================================
+-- Uploads: Add new fields and composite indexes
+-- ============================================
+ALTER TABLE uploads ADD COLUMN IF NOT EXISTS tag_name VARCHAR(255);
+ALTER TABLE uploads ADD COLUMN IF NOT EXISTS user_agent VARCHAR(512);
+ALTER TABLE uploads ADD COLUMN IF NOT EXISTS duration_ms INTEGER;
+ALTER TABLE uploads ADD COLUMN IF NOT EXISTS deduplicated BOOLEAN DEFAULT false;
+ALTER TABLE uploads ADD COLUMN IF NOT EXISTS checksum_verified BOOLEAN DEFAULT true;
+
+CREATE INDEX IF NOT EXISTS idx_uploads_package_uploaded_at ON uploads(package_id, uploaded_at DESC);
+CREATE INDEX IF NOT EXISTS idx_uploads_uploaded_by_at ON uploads(uploaded_by, uploaded_at DESC);
+
+-- ============================================
+-- Audit Logs: Add composite indexes and GIN index
+-- ============================================
+CREATE INDEX IF NOT EXISTS idx_audit_logs_resource_timestamp ON audit_logs(resource, timestamp DESC);
+CREATE INDEX IF NOT EXISTS idx_audit_logs_user_timestamp ON audit_logs(user_id, timestamp DESC);
+CREATE INDEX IF NOT EXISTS idx_audit_logs_details ON audit_logs USING GIN (details);
+
+-- ============================================
+-- Projects: Add partial index for public projects
+-- ============================================
+CREATE INDEX IF NOT EXISTS idx_projects_public ON projects(name) WHERE is_public = true;
+
+-- ============================================
+-- Triggers: Update tag_changes trigger for change_type
+-- ============================================
+CREATE OR REPLACE FUNCTION track_tag_changes()
+RETURNS TRIGGER AS $$
+BEGIN
+    IF TG_OP = 'UPDATE' AND OLD.artifact_id != NEW.artifact_id THEN
+        INSERT INTO tag_history (id, tag_id, old_artifact_id, new_artifact_id, change_type, changed_at, changed_by)
+        VALUES (gen_random_uuid(), NEW.id, OLD.artifact_id, NEW.artifact_id, 'update', NOW(), NEW.created_by);
+    END IF;
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+-- ============================================
+-- Triggers: Auto-update updated_at timestamps
+-- ============================================
+CREATE OR REPLACE FUNCTION update_updated_at_column()
+RETURNS TRIGGER AS $$
+BEGIN
+    NEW.updated_at = NOW();
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+-- Drop triggers if they exist, then recreate
+DROP TRIGGER IF EXISTS projects_updated_at_trigger ON projects;
+CREATE TRIGGER projects_updated_at_trigger
+    BEFORE UPDATE ON projects
+    FOR EACH ROW
+    EXECUTE FUNCTION update_updated_at_column();
+
+DROP TRIGGER IF EXISTS packages_updated_at_trigger ON packages;
+CREATE TRIGGER packages_updated_at_trigger
+    BEFORE UPDATE ON packages
+    FOR EACH ROW
+    EXECUTE FUNCTION update_updated_at_column();
+
+DROP TRIGGER IF EXISTS tags_updated_at_trigger ON tags;
+CREATE TRIGGER tags_updated_at_trigger
+    BEFORE UPDATE ON tags
+    FOR EACH ROW
+    EXECUTE FUNCTION update_updated_at_column();
+
+-- ============================================
+-- Triggers: Maintain artifact ref_count accuracy
+-- ============================================
+CREATE OR REPLACE FUNCTION increment_artifact_ref_count()
+RETURNS TRIGGER AS $$
+BEGIN
+    UPDATE artifacts SET ref_count = ref_count + 1 WHERE id = NEW.artifact_id;
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE OR REPLACE FUNCTION decrement_artifact_ref_count()
+RETURNS TRIGGER AS $$
+BEGIN
+    UPDATE artifacts SET ref_count = ref_count - 1 WHERE id = OLD.artifact_id;
+    RETURN OLD;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE OR REPLACE FUNCTION update_artifact_ref_count()
+RETURNS TRIGGER AS $$
+BEGIN
+    IF OLD.artifact_id != NEW.artifact_id THEN
+        UPDATE artifacts SET ref_count = ref_count - 1 WHERE id = OLD.artifact_id;
+        UPDATE artifacts SET ref_count = ref_count + 1 WHERE id = NEW.artifact_id;
+    END IF;
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+-- Note: ref_count triggers on tags table
+-- These track how many tags reference each artifact
+DROP TRIGGER IF EXISTS tags_ref_count_insert_trigger ON tags;
+CREATE TRIGGER tags_ref_count_insert_trigger
+    AFTER INSERT ON tags
+    FOR EACH ROW
+    EXECUTE FUNCTION increment_artifact_ref_count();
+
+DROP TRIGGER IF EXISTS tags_ref_count_delete_trigger ON tags;
+CREATE TRIGGER tags_ref_count_delete_trigger
+    AFTER DELETE ON tags
+    FOR EACH ROW
+    EXECUTE FUNCTION decrement_artifact_ref_count();
+
+DROP TRIGGER IF EXISTS tags_ref_count_update_trigger ON tags;
+CREATE TRIGGER tags_ref_count_update_trigger
+    AFTER UPDATE ON tags
+    FOR EACH ROW
+    EXECUTE FUNCTION update_artifact_ref_count();