diff --git a/.gitignore b/.gitignore
index 13cf476..df86f0d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -21,3 +21,6 @@ phpcs.xml
 .idea/**/.name
 .idea/**/codeStyles
 .idea/**/php.xml
+
+## Tests
+tests/assets/test-sqlite.db
diff --git a/composer.json b/composer.json
index 715b6f7..62947d5 100644
--- a/composer.json
+++ b/composer.json
@@ -40,6 +40,9 @@
 		"phpcompatibility/phpcompatibility-wp": "^2.1",
 		"overtrue/phplint": "^3.4"
 	},
+	"suggest": {
+		"ext-pdo": "PDO is required to use the SQLite cache provider"
+	},
 	"scripts": {
 		"suite": [
 			"composer test",
diff --git a/phpstan.dist.neon b/phpstan.dist.neon
index 278e025..aaa5d63 100644
--- a/phpstan.dist.neon
+++ b/phpstan.dist.neon
@@ -2,6 +2,7 @@ includes:
         - vendor/szepeviktor/phpstan-wordpress/extension.neon
 
 parameters:
+    editorUrl: 'phpstorm://open?file=%%file%%&line=%%line%%'
     level: 5
     paths:
         - src
diff --git a/src/Cache/ArrayCacheProvider.php b/src/Cache/ArrayCacheProvider.php
index acf0248..a9f387d 100644
--- a/src/Cache/ArrayCacheProvider.php
+++ b/src/Cache/ArrayCacheProvider.php
@@ -4,6 +4,8 @@
 
 use DataKit\DataViews\Clock\Clock;
 use DataKit\DataViews\Clock\SystemClock;
+use DateInterval;
+use Exception;
 
 /**
  * Cache provider backed by an array.
@@ -12,24 +14,24 @@
  *
  * @since $ver$
  */
-final class ArrayCacheProvider implements CacheProvider {
+final class ArrayCacheProvider extends BaseCacheProvider {
 	/**
 	 * The cached items.
 	 *
 	 * @since $ver$
 	 *
-	 * @var array
+	 * @var CacheItem[]
 	 */
-	private array $items;
+	private array $items = [];
 
 	/**
-	 * The clock instance.
+	 * Contains the reference to the tags with their tagged cache keys.
 	 *
 	 * @since $ver$
 	 *
-	 * @var Clock
+	 * @var array<string, string[]>
 	 */
-	private Clock $clock;
+	private array $tags = [];
 
 	/**
 	 * Creates an Array cache provider.
@@ -37,11 +39,11 @@ final class ArrayCacheProvider implements CacheProvider {
 	 * @since $ver$
 	 *
 	 * @param Clock|null $clock The clock instance.
-	 * @param array      $items The pre-filled cache items.
 	 */
-	public function __construct( ?Clock $clock = null, array $items = [] ) {
+	public function __construct( ?Clock $clock = null ) {
+		parent::__construct( $clock );
+
 		$this->clock = $clock ?? new SystemClock();
-		$this->items = $items;
 	}
 
 	/**
@@ -49,12 +51,18 @@ public function __construct( ?Clock $clock = null, array $items = [] ) {
 	 *
 	 * @since $ver$
 	 */
-	public function set( string $key, $value, ?int $ttl = null ): void {
-		$time = $ttl
-			? ( $this->clock->now()->getTimestamp() + $ttl )
-			: null;
+	public function set( string $key, $value, ?int $ttl = null, array $tags = [] ): void {
+		try {
+			$time = (int) $ttl > 0
+				? ( $this->clock->now()->add( new DateInterval( 'PT' . $ttl . 'S' ) ) )
+				: null;
+		} catch ( Exception $e ) {
+			throw new \InvalidArgumentException( $e->getMessage(), $e->getCode(), $e );
+		}
 
-		$this->items[ $key ] = compact( 'value', 'time' );
+		$this->items[ $key ] = new CacheItem( $key, $value, $time, $tags );
+
+		$this->add_tags( $key, $tags );
 	}
 
 	/**
@@ -62,16 +70,10 @@ public function set( string $key, $value, ?int $ttl = null ): void {
 	 *
 	 * @since $ver$
 	 */
-	public function get( string $key, $fallback = null ) {
-		$item = $this->items[ $key ] ?? [];
-
-		if ( $this->is_expired( $item ) ) {
-			unset( $this->items[ $key ] );
-
-			return $fallback;
-		}
+	public function delete( string $key ): bool {
+		unset( $this->items[ $key ] );
 
-		return $item['value'] ?? $fallback;
+		return true;
 	}
 
 	/**
@@ -79,17 +81,16 @@ public function get( string $key, $fallback = null ) {
 	 *
 	 * @since $ver$
 	 */
-	public function has( string $key ): bool {
-		if (
-			isset( $this->items[ $key ] )
-			&& ! $this->is_expired( $this->items[ $key ] )
-		) {
-			return true;
-		}
+	public function delete_by_tags( array $tags ): bool {
+		foreach ( $tags as $tag ) {
+			foreach ( $this->tags[ $tag ] ?? [] as $key ) {
+				$this->delete( $key );
+			}
 
-		unset( $this->items[ $key ] );
+			unset( $this->tags[ $tag ] );
+		}
 
-		return false;
+		return true;
 	}
 
 	/**
@@ -97,36 +98,39 @@ public function has( string $key ): bool {
 	 *
 	 * @since $ver$
 	 */
-	public function delete( string $key ): bool {
-		unset( $this->items[ $key ] );
+	public function clear(): bool {
+		$this->items = [];
+		$this->tags  = [];
 
 		return true;
 	}
 
 	/**
-	 * @inheritDoc
+	 * Records a key for all provided tags.
 	 *
 	 * @since $ver$
+	 *
+	 * @param string $key  The key to tag.
+	 * @param array  $tags The tags.
 	 */
-	public function clear(): bool {
-		$this->items = [];
+	private function add_tags( string $key, array $tags ): void {
+		foreach ( $tags as $tag ) {
+			if ( ! is_string( $tag ) ) {
+				throw new \InvalidArgumentException( 'A tag must be a string.' );
+			}
 
-		return true;
+			$this->tags[ $tag ] ??= [];
+
+			$this->tags[ $tag ] = array_unique( array_merge( $this->tags[ $tag ], [ $key ] ) );
+		}
 	}
 
 	/**
-	 * Returns whether the provided cache item is expired.
+	 * @inheritDoc
 	 *
 	 * @since $ver$
-	 *
-	 * @param array $item The cache item.
-	 *
-	 * @return bool Whether the cache is expired.
 	 */
-	private function is_expired( array $item ): bool {
-		return (
-			( $item['time'] ?? null )
-			&& $this->clock->now()->getTimestamp() > $item['time']
-		);
+	protected function doGet( string $key ): ?CacheItem {
+		return $this->items[ $key ] ?? null;
 	}
 }
diff --git a/src/Cache/BaseCacheProvider.php b/src/Cache/BaseCacheProvider.php
new file mode 100644
index 0000000..38ab1fd
--- /dev/null
+++ b/src/Cache/BaseCacheProvider.php
@@ -0,0 +1,72 @@
+<?php
+
+namespace DataKit\DataViews\Cache;
+
+use DataKit\DataViews\Clock\Clock;
+use DataKit\DataViews\Clock\SystemClock;
+
+/**
+ * An abstract cache provider that implements default logic.
+ *
+ * @since $ver$
+ */
+abstract class BaseCacheProvider implements CacheProvider {
+	/**
+	 * The clock.
+	 *
+	 * @since $ver$
+	 * @var Clock
+	 */
+	protected Clock $clock;
+
+	/**
+	 * Creates the base cache provider.
+	 *
+	 * @since $ver$
+	 *
+	 * @param Clock|null $clock The clock.
+	 */
+	public function __construct( ?Clock $clock = null ) {
+		$this->clock = $clock ?? new SystemClock();
+	}
+
+	/**
+	 * Returns the {@see CacheItem} if found by key.
+	 *
+	 * @param string $key The key.
+	 *
+	 * @return CacheItem|null The cache item.
+	 */
+	abstract protected function doGet( string $key ): ?CacheItem;
+
+	/**
+	 * @inheritDoc
+	 * @since $ver$
+	 */
+	public function get( string $key, $fallback = null ) {
+		$item = $this->doGet( $key );
+		if ( ! $item || $item->is_expired( $this->clock->now() ) ) {
+			$this->delete( $key );
+
+			return $fallback;
+		}
+
+		return $item->value();
+	}
+
+	/**
+	 * @inheritDoc
+	 * @since $ver$
+	 */
+	public function has( string $key ): bool {
+		$item = $this->doGet( $key );
+
+		if ( ! $item || $item->is_expired( $this->clock->now() ) ) {
+			$this->delete( $key );
+
+			return false;
+		}
+
+		return true;
+	}
+}
diff --git a/src/Cache/CacheItem.php b/src/Cache/CacheItem.php
new file mode 100644
index 0000000..6f07cfb
--- /dev/null
+++ b/src/Cache/CacheItem.php
@@ -0,0 +1,143 @@
+<?php
+
+namespace DataKit\DataViews\Cache;
+
+use DateTimeImmutable;
+use DateTimeInterface;
+
+/**
+ * Represents a single cache item.
+ *
+ * @since $ver$
+ */
+final class CacheItem {
+	/**
+	 * The key for the cache item.
+	 *
+	 * @since $ver$
+	 *
+	 * @var string
+	 */
+	private string $key;
+
+	/**
+	 * The cached value.
+	 *
+	 * @since $ver$
+	 *
+	 * @var mixed
+	 */
+	private $value;
+
+	/**
+	 * The unix timestamp when the cache expires.
+	 *
+	 * @since $ver$
+	 *
+	 * @var DateTimeInterface|null
+	 */
+	private ?DateTimeInterface $expires_at;
+
+	/**
+	 * The tags for this cache item.
+	 *
+	 * @since $ver$
+	 *
+	 * @var string[]
+	 */
+	private array $tags;
+
+	/**
+	 * Creates the Cache Item.
+	 *
+	 * @param string                 $key        The cache key.
+	 * @param mixed                  $value      The cached value.
+	 * @param DateTimeInterface|null $expires_at The timestamp the cache item expires.
+	 * @param string[]               $tags       The tags for the cache item.
+	 */
+	public function __construct( string $key, $value, ?DateTimeInterface $expires_at = null, array $tags = [] ) {
+		$this->set_key( $key );
+		$this->value      = $value;
+		$this->expires_at = $expires_at;
+
+		$this->add_tags( ...$tags );
+	}
+
+	/**
+	 * Sets the key, and ensures it is valid.
+	 *
+	 * @since $ver$
+	 *
+	 * @param string $key The cache key.
+	 */
+	private function set_key( string $key ): void {
+		if ( strlen( $key ) > 64 ) {
+			throw new \InvalidArgumentException( 'Cache keys may not exceed a length of 64 characters.' );
+		}
+
+		if ( preg_replace( '/[^a-z0-9_.]+/i', '', $key ) !== $key ) {
+			throw new \InvalidArgumentException( 'Cache keys may only contain a-z, A-Z, 0-9, underscores (_) and periods (.).' );
+		}
+
+		$this->key = $key;
+	}
+
+	/**
+	 * Returns the key for the cache item.
+	 *
+	 * @since $ver$
+	 *
+	 * @return string The cache key.
+	 */
+	public function key(): string {
+		return $this->key;
+	}
+
+	/**
+	 * Returns the value on the CacheItem.
+	 *
+	 * @since $ver$
+	 *
+	 * @return mixed The cached value.
+	 */
+	public function value() {
+		return $this->value;
+	}
+
+	/**
+	 * Returns the tags for the cache item.
+	 *
+	 * @since $ver$
+	 *
+	 * @return string[] The tags.
+	 */
+	public function tags(): array {
+		return $this->tags;
+	}
+
+	/**
+	 * Returns whether the cache item is expired.
+	 *
+	 * @param DateTimeImmutable $now The date time to test against.
+	 *
+	 * @return bool Whether the cache item is expired.
+	 */
+	public function is_expired( DateTimeImmutable $now ): bool {
+		if ( null === $this->expires_at ) {
+			return false;
+		}
+
+		return $now > $this->expires_at;
+	}
+
+	/**
+	 * Ensures all tags are strings.
+	 *
+	 * @since $ver$
+	 *
+	 * @param string ...$tags The tags.
+	 */
+	private function add_tags( string ...$tags ): void {
+		$this->tags = $tags;
+	}
+}
diff --git a/src/Cache/CacheProvider.php b/src/Cache/CacheProvider.php
index ab5565f..84d68c8 100644
--- a/src/Cache/CacheProvider.php
+++ b/src/Cache/CacheProvider.php
@@ -17,7 +17,7 @@ interface CacheProvider {
 	 * @param mixed    $value The value to cache.
 	 * @param int|null $ttl   The time to live in seconds.
 	 */
-	public function set( string $key, $value, ?int $ttl = null ): void;
+	public function set( string $key, $value, ?int $ttl = null, array $tags = [] ): void;
 
 	/**
 	 * Retrieves the value from the cache, or the default if no value is stored.
@@ -56,6 +56,17 @@ public function has( string $key ): bool;
 	 */
 	public function delete( string $key ): bool;
 
+	/**
+	 * .Deletes any entries tagged with one of the provided tags.
+	 *
+	 * @since $ver$
+	 *
+	 * @param string[] $tags The tags to clear.
+	 *
+	 * @return bool Whether the deletion of the cache items was successful.
+	 */
+	public function delete_by_tags( array $tags ): bool;
+
 	/**
 	 * Clears the entire cache.
 	 *
diff --git a/src/Cache/SqliteCacheProvider.php b/src/Cache/SqliteCacheProvider.php
new file mode 100644
index 0000000..56a817b
--- /dev/null
+++ b/src/Cache/SqliteCacheProvider.php
@@ -0,0 +1,224 @@
+<?php
+
+namespace DataKit\DataViews\Cache;
+
+use DataKit\DataViews\Clock\Clock;
+use DateInterval;
+use DateTimeImmutable;
+use Exception;
+use PDO;
+use RuntimeException;
+
+/**
+ * A cache provider backed by SQLite 3 through PDO.
+ *
+ * @since $ver$
+ */
+final class SqliteCacheProvider extends BaseCacheProvider {
+	/**
+	 * The database connection.
+	 *
+	 * @since $ver$
+	 *
+	 * @var PDO
+	 */
+	private PDO $db;
+
+	/**
+	 * The file path to the SQLite DB.
+	 *
+	 * @since $ver$
+	 *
+	 * @var string
+	 */
+	private string $file_path;
+
+	/**
+	 * Creates the SQLite Cache Provider.
+	 *
+	 * @since $ver$
+	 *
+	 * @param string $file_path The path to the SQL file.
+	 */
+	public function __construct( string $file_path, ?Clock $clock = null ) {
+		if ( ! class_exists( PDO::class ) ) {
+			throw new RuntimeException( 'PDO is not installed.' );
+		}
+
+		parent::__construct( $clock );
+		$this->file_path = $file_path;
+	}
+
+	/**
+	 * Creates the tables on the database.
+	 *
+	 * @since $ver$
+	 */
+	private function create_tables(): void {
+		$this->db->exec(
+			'CREATE TABLE IF NOT EXISTS `items` (
+				item_key VARCHAR(64) NOT NULL PRIMARY KEY,
+    			item_value TEXT,
+    			expires_at VARCHAR(100) 
+			);'
+		);
+
+		$this->db->exec(
+			'CREATE TABLE if NOT EXISTS `tags` (
+				item_tag VARCHAR( 64 ) NOT null,
+    			item_key VARCHAR( 64 ) NOT null,
+    			PRIMARY KEY( item_tag, item_key )
+			);'
+		);
+	}
+
+	/**
+	 * Lazily creates the connection to the database.
+	 *
+	 * @since $ver$
+	 */
+	private function init(): void {
+		if ( ! isset( $this->db ) ) {
+			$this->db = new PDO( 'sqlite:' . $this->file_path );
+			$this->create_tables();
+		}
+	}
+
+	/**
+	 * @inheritDoc
+	 * @since $ver$
+	 */
+	public function set( string $key, $value, ?int $ttl = null, array $tags = [] ): void {
+		$this->init();
+
+		try {
+			$time = (int) $ttl > 0
+				? ( $this->clock->now()->add( new DateInterval( 'PT' . $ttl . 'S' ) ) )
+				: null;
+		} catch ( Exception $e ) {
+			throw new \InvalidArgumentException( $e->getMessage(), $e->getCode(), $e );
+		}
+
+		$this->db->prepare(
+			'INSERT INTO items (item_key, item_value, expires_at) VALUES (:key, :value, :expires_at) 
+             ON CONFLICT (item_key) DO UPDATE SET item_value = :value, expires_at = :expires_at'
+		)->execute(
+			[
+				'key'        => $key,
+				'value'      => json_encode( $value, JSON_THROW_ON_ERROR ),
+				'expires_at' => $time ? $time->format( 'c' ) : null,
+			]
+		);
+
+		$this->add_tags( $key, $tags );
+	}
+
+	/**
+	 * @inheritDoc
+	 *
+	 * @since $ver$
+	 */
+	protected function doGet( string $key ): ?CacheItem {
+		$this->init();
+
+		$statement = $this->db->prepare( 'SELECT * FROM items WHERE item_key = :key' );
+		$statement->execute( [ 'key' => $key ] );
+		$result = $statement->fetch( PDO::FETCH_ASSOC );
+		if ( ! $result ) {
+			return null;
+		}
+
+		return new CacheItem(
+			$key,
+			json_decode( $result['item_value'], true ),
+			$result['expires_at'] ? new DateTimeImmutable( $result['expires_at'] ) : null
+		);
+	}
+
+	/**
+	 * @inheritDoc
+	 * @since $ver$
+	 */
+	public function delete( string $key ): bool {
+		$this->init();
+
+		return $this->db
+			->prepare( 'DELETE FROM items WHERE item_key = :key' )
+			->execute( [ 'key' => $key ] );
+	}
+
+	/**
+	 * @inheritDoc
+	 * @since $ver$
+	 */
+	public function delete_by_tags( array $tags ): bool {
+		$this->init();
+
+		if ( ! $tags ) {
+			return true;
+		}
+
+		$tags_string = implode(
+			',',
+			array_map(
+				fn( string $tag ): string => $this->db->quote( $tag ),
+				$tags
+			)
+		);
+
+		// Remove items.
+		$this->db->exec(
+			"DELETE FROM items WHERE item_key IN (
+                SELECT item_key FROM tags WHERE item_tag IN ($tags_string)
+            );"
+		);
+
+		// Remove tags.
+		$this->db->exec( "DELETE FROM tags WHERE item_tag IN ($tags_string)" );
+
+		return true;
+	}
+
+	/**
+	 * @inheritDoc
+	 * @since $ver$
+	 */
+	public function clear(): bool {
+		if ( file_exists( $this->file_path ) ) {
+			@unlink( $this->file_path ); //@phpcs:ignore WordPress.WP.AlternativeFunctions.unlink_unlink, WordPress.PHP.NoSilencedErrors.Discouraged
+			unset( $this->db );
+		}
+
+		$this->init();
+
+		return true;
+	}
+
+	/**
+	 * Records a key for all provided tags.
+	 *
+	 * @since $ver$
+	 *
+	 * @param string $key  The key to tag.
+	 * @param array  $tags The tags.
+	 */
+	private function add_tags( string $key, array $tags ): void {
+		if ( ! $tags ) {
+			return;
+		}
+
+		$query  = 'INSERT INTO tags (item_key, item_tag) VALUES ';
+		$values = [];
+		$parts  = [];
+
+		foreach ( $tags as $tag ) {
+			$values[] = $key;
+			$values[] = $tag;
+
+			$parts[] = '(?,?)';
+		}
+
+		$this->db->prepare( $query . implode( ',', $parts ) )
+			->execute( $values );
+	}
+}
diff --git a/src/Clock/Clock.php b/src/Clock/Clock.php
index b7d7fc9..20360c2 100644
--- a/src/Clock/Clock.php
+++ b/src/Clock/Clock.php
@@ -2,7 +2,7 @@
 
 namespace DataKit\DataViews\Clock;
 
-use DateTimeInterface;
+use DateTimeImmutable;
 
 /**
  * Object that represents a clock.
@@ -15,5 +15,5 @@ interface Clock {
 	 *
 	 * @since $ver$
 	 */
-	public function now(): DateTimeInterface;
+	public function now(): DateTimeImmutable;
 }
diff --git a/src/Data/CachedDataSource.php b/src/Data/CachedDataSource.php
index 9efb3ba..3ac008a 100644
--- a/src/Data/CachedDataSource.php
+++ b/src/Data/CachedDataSource.php
@@ -60,6 +60,17 @@ public function id(): string {
 		return $this->inner->id();
 	}
 
+	/**
+	 * Returns the tags used for this data source.
+	 *
+	 * @since $ver$
+	 *
+	 * @return string[] The tags.
+	 */
+	private function get_tag_keys(): array {
+		return [ 'DATASOURCE_' . $this->get_cache_key() ];
+	}
+
 	/**
 	 * Returns a calculated key based on a set of arguments.
 	 *
@@ -73,7 +84,7 @@ private function get_cache_key( ...$arguments ): string {
 		$arguments[] = $this->inner->id();
 
 		try {
-			return md5( json_encode( $arguments, JSON_THROW_ON_ERROR ) );
+			return md5( json_encode( array_values( array_filter( $arguments ) ), JSON_THROW_ON_ERROR ) );
 		} catch ( JsonException $e ) {
 			throw new InvalidArgumentException(
 				'The cache key could not be generated based on the provide arguments',
@@ -94,8 +105,7 @@ private function get_cache_key( ...$arguments ): string {
 	 */
 	private function get_filter_aware_cache_key( ...$arguments ): string {
 		$arguments[] = $this->filters ? $this->filters->to_array() : null;
-		$arguments[] = $this->sort ? $this->sort->to_array() : null;
-		$arguments[] = $this->search;
+		$arguments[] = (string) $this->search;
 
 		return $this->get_cache_key( ...$arguments );
 	}
@@ -119,8 +129,7 @@ private function fetch( string $cache_key, callable $retrieve_result ) {
 
 		$result = $retrieve_result();
 
-		// Todo: record this key on a group cache, so we can invalidate all cached keys in one swoop.
-		$this->cache->set( $cache_key, $result );
+		$this->cache->set( $cache_key, $result, null, $this->get_tag_keys() );
 
 		return $result;
 	}
@@ -131,7 +140,12 @@ private function fetch( string $cache_key, callable $retrieve_result ) {
 	 * @since $ver$
 	 */
 	public function get_data_ids( int $limit = 20, int $offset = 0 ): array {
-		$key = $this->get_filter_aware_cache_key( __FUNCTION__, $limit, $offset );
+		$key = $this->get_filter_aware_cache_key(
+			__FUNCTION__,
+			$this->sort ? $this->sort->to_array() : null,
+			$limit,
+			$offset
+		);
 
 		return $this->fetch(
 			$key,
@@ -254,7 +268,6 @@ public function delete_data_by_id( string ...$ids ): void {
 	 * @return bool Whether the cache was cleared.
 	 */
 	public function clear_cache(): bool {
-		// Todo: only clear the cache for the keys for this data source.
-		return $this->cache->clear();
+		return $this->cache->delete_by_tags( $this->get_tag_keys() );
 	}
 }
diff --git a/src/Field/FilterableField.php b/src/Field/FilterableField.php
index 19c9554..7ee1f63 100644
--- a/src/Field/FilterableField.php
+++ b/src/Field/FilterableField.php
@@ -35,7 +35,7 @@ abstract class FilterableField extends Field {
 	 *
 	 * @param Operator ...$operators The operators.
 	 *
-	 * @return self A new instance with the filters applied.
+	 * @return static A new instance with the filters applied.
 	 */
 	public function filterable_by( Operator ...$operators ) {
 		$clone            = clone $this;
diff --git a/tests/Cache/AbstractCacheProviderTest.php b/tests/Cache/AbstractCacheProviderTest.php
new file mode 100644
index 0000000..adb7868
--- /dev/null
+++ b/tests/Cache/AbstractCacheProviderTest.php
@@ -0,0 +1,115 @@
+<?php
+
+namespace DataKit\DataViews\Tests\Cache;
+
+use DataKit\DataViews\Cache\CacheProvider;
+use DataKit\DataViews\Clock\Clock;
+use DataKit\DataViews\Tests\Clock\FrozenClock;
+use PHPUnit\Framework\TestCase;
+
+abstract class AbstractCacheProviderTest extends TestCase {
+
+	abstract protected function create_provider( ?Clock $clock ): CacheProvider;
+
+	/**
+	 * Test case entire array cache.
+	 *
+	 * @since $ver$
+	 */
+	public function test_cache(): void {
+		$cache = $this->create_provider( null );
+
+		self::assertFalse( $cache->has( 'some_key' ) );
+		$cache->set( 'some_key', 'A value' );
+		$cache->set( 'other_key', 'Other value' );
+
+		self::assertTrue( $cache->has( 'some_key' ) );
+		self::assertTrue( $cache->has( 'other_key' ) );
+
+		self::assertSame( 'A value', $cache->get( 'some_key', 'different default' ) );
+		self::assertSame( 'different default', $cache->get( 'invalid', 'different default' ) );
+		self::assertNull( $cache->get( 'invalid' ) );
+
+		self::assertTrue( $cache->delete( 'some_key' ) );
+		self::assertFalse( $cache->has( 'some_key' ) );
+		self::assertNull( $cache->get( 'some_key' ) );
+
+		self::assertTrue( $cache->clear() );
+		self::assertFalse( $cache->has( 'other_key' ) );
+	}
+
+	/**
+	 * Test case for a TTL.
+	 *
+	 * @return void
+	 */
+	public function test_ttl(): void {
+		$clock = new FrozenClock( '2024-06-27 12:34:56' );
+		$cache = $this->create_provider( $clock );
+
+		$cache->set( 'some_key', $value = 'This value is stored for 5 seconds.', 5 );
+		$cache->set( 'another_key', $value, 5 );
+
+		self::assertTrue( $cache->has( 'some_key' ) );
+		self::assertSame( $value, $cache->get( 'another_key' ) );
+
+		$clock->travel_to( '2024-06-27 13:00:00' );
+		self::assertFalse( $cache->has( 'some_key' ) );
+		self::assertNull( $cache->get( 'another_key' ) );
+
+		$clock->travel_to( '2024-06-27 12:34:54' ); // back in time.
+		self::assertFalse( $cache->has( 'some_key' ) );
+	}
+
+	public static function dataprovider_for_test_tags(): array {
+		return [
+			'none'      => [
+				[],
+				[ 'key_1_1', 'key_1_2', 'key_2_1', 'key_2_2' ],
+			],
+			'tag_1'     => [
+				[ 'tag_1' ],
+				[ 'key_2_1', 'key_2_2' ],
+			],
+			'tag_2'     => [
+				[ 'tag_2' ],
+				[ 'key_1_1', 'key_1_2' ],
+			],
+			'both tags' => [
+				[ 'tag_1', 'tag_2' ],
+				[],
+			],
+		];
+	}
+
+	/**
+	 * Test case for cache items with tags.
+	 *
+	 * @since        $ver$
+	 *
+	 * @param array $tags_to_delete The tags to delete during the test.
+	 * @param array $expected_keys  The keys expected to remain after the deletion.
+	 *
+	 * @dataProvider dataprovider_for_test_tags The data provider.
+	 */
+	public function test_tags( array $tags_to_delete, array $expected_keys ): void {
+		$cache = $this->create_provider( null );
+		$keys  = [ 'key_1_1', 'key_1_2', 'key_2_1', 'key_2_2' ];
+
+		$cache->set( 'key_1_1', 'value 1.1', null, [ 'tag_1' ] );
+		$cache->set( 'key_1_2', 'value 1.2', null, [ 'tag_1' ] );
+
+		$cache->set( 'key_2_1', 'value 2.1', null, [ 'tag_2' ] );
+		$cache->set( 'key_2_2', 'value 2.2', null, [ 'tag_2' ] );
+
+		foreach ( $keys as $key ) {
+			self::assertTrue( $cache->has( $key ) );
+		}
+
+		$cache->delete_by_tags( $tags_to_delete );
+
+		foreach ( $keys as $key ) {
+			self::assertEquals( in_array( $key, $expected_keys, true ), $cache->has( $key ) );
+		}
+	}
+}
diff --git a/tests/Cache/ArrayCacheProviderTest.php b/tests/Cache/ArrayCacheProviderTest.php
index bd26493..62562b2 100644
--- a/tests/Cache/ArrayCacheProviderTest.php
+++ b/tests/Cache/ArrayCacheProviderTest.php
@@ -3,62 +3,21 @@
 namespace DataKit\DataViews\Tests\Cache;
 
 use DataKit\DataViews\Cache\ArrayCacheProvider;
-use DataKit\DataViews\Tests\Clock\FrozenClock;
-use PHPUnit\Framework\TestCase;
+use DataKit\DataViews\Cache\CacheProvider;
+use DataKit\DataViews\Clock\Clock;
 
 /**
- * Unit tests for {@see ArrayCacheProvider}
+ * Unit tests for {@see ArrayCacheProvider}.
  *
  * @since $ver$
  */
-final class ArrayCacheProviderTest extends TestCase {
+final class ArrayCacheProviderTest extends AbstractCacheProviderTest {
 	/**
-	 * Test case entire array cache.
+	 * @inheritDoc
 	 *
 	 * @since $ver$
 	 */
-	public function test_cache() : void {
-		$cache = new ArrayCacheProvider();
-
-		self::assertFalse( $cache->has( 'some-key' ) );
-		$cache->set( 'some-key', 'A value' );
-		$cache->set( 'other-key', 'Other value' );
-
-		self::assertTrue( $cache->has( 'some-key' ) );
-		self::assertTrue( $cache->has( 'other-key' ) );
-
-		self::assertSame( 'A value', $cache->get( 'some-key', 'different default' ) );
-		self::assertSame( 'different default', $cache->get( 'invalid', 'different default' ) );
-		self::assertNull( $cache->get( 'invalid' ) );
-
-		self::assertTrue( $cache->delete( 'some-key' ) );
-		self::assertFalse( $cache->has( 'some-key' ) );
-		self::assertNull( $cache->get( 'some-key' ) );
-
-		self::assertTrue( $cache->clear() );
-		self::assertFalse( $cache->has( 'other-key' ) );
-	}
-
-	/**
-	 * Test case for a TTL.
-	 *
-	 * @return void
-	 */
-	public function test_ttl() : void {
-		$clock = new FrozenClock( '2024-06-27 12:34:56' );
-		$cache = new ArrayCacheProvider( $clock );
-
-		$cache->set( 'some-key', $value = 'This value is stored for 5 seconds.', 5 );
-		$cache->set( 'another-key', $value, 5 );
-
-		self::assertTrue( $cache->has( 'some-key' ) );
-		self::assertSame( $value, $cache->get( 'another-key' ) );
-
-		$clock->travel_to( '2024-06-27 13:00:00' );
-		self::assertFalse( $cache->has( 'some-key' ) );
-		self::assertNull( $cache->get( 'another-key' ) );
-
-		$clock->travel_to( '2024-06-27 12:34:54' ); // back in time.
-		self::assertFalse( $cache->has( 'some-key' ) );
+	protected function create_provider( ?Clock $clock ): CacheProvider {
+		return new ArrayCacheProvider( $clock );
 	}
 }
diff --git a/tests/Cache/CacheItemTest.php b/tests/Cache/CacheItemTest.php
new file mode 100644
index 0000000..3aad938
--- /dev/null
+++ b/tests/Cache/CacheItemTest.php
@@ -0,0 +1,35 @@
+<?php
+
+namespace DataKit\DataViews\Tests\Cache;
+
+use DataKit\DataViews\Cache\CacheItem;
+use DataKit\DataViews\Tests\Clock\FrozenClock;
+use DateTimeImmutable;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Unit tests for {@see CacheItem}
+ *
+ * @since $ver$
+ */
+final class CacheItemTest extends TestCase {
+	/**
+	 * Test case for
+	 *
+	 * @since $ver$
+	 */
+	public function test_cache_item(): void {
+		$clock      = new FrozenClock( '2024-09-10 10:35:00' );
+		$timestamp  = new DateTimeImmutable('2024-09-10 10:35:05');
+		$serialized = serialize( new CacheItem( 'key_1', 'value-1', $timestamp, [ 'tag_1', 'tag_2' ] ) );
+		$item       = unserialize( $serialized );
+
+		self::assertSame( 'key_1', $item->key() );
+		self::assertSame( 'value-1', $item->value() );
+		self::assertSame( [ 'tag_1', 'tag_2' ], $item->tags() );
+
+		self::assertFalse( $item->is_expired( $clock->now() ) );
+		$clock->travel_to( '2024-09-10 10:36:00' );
+		self::assertTrue( $item->is_expired( $clock->now() ) );
+	}
+}
diff --git a/tests/Cache/SqliteCacheProviderTest.php b/tests/Cache/SqliteCacheProviderTest.php
new file mode 100644
index 0000000..b062b85
--- /dev/null
+++ b/tests/Cache/SqliteCacheProviderTest.php
@@ -0,0 +1,28 @@
+<?php
+
+namespace DataKit\DataViews\Tests\Cache;
+
+use DataKit\DataViews\Cache\CacheProvider;
+use DataKit\DataViews\Cache\SqliteCacheProvider;
+use DataKit\DataViews\Clock\Clock;
+use DataKit\DataViews\Tests\Clock\FrozenClock;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Unit tests for {@see SqliteCacheProvider}.
+ *
+ * @since $ver$
+ */
+final class SqliteCacheProviderTest extends AbstractCacheProviderTest {
+	/**
+	 * @inheritDoc
+	 *
+	 * @since $ver$
+	 */
+	protected function create_provider( ?Clock $clock ): CacheProvider {
+		$path = dirname( __DIR__ ) . '/assets/test-sqlite.db';
+		@unlink( $path ); // Clear for tests.
+
+		return new SqliteCacheProvider( $path, $clock );
+	}
+}
diff --git a/tests/Data/CachedDataSourceTest.php b/tests/Data/CachedDataSourceTest.php
index 933e7a3..cb2b1ac 100644
--- a/tests/Data/CachedDataSourceTest.php
+++ b/tests/Data/CachedDataSourceTest.php
@@ -2,6 +2,7 @@
 
 namespace DataKit\DataViews\Tests\Data;
 
+use Closure;
 use DataKit\DataViews\Cache\ArrayCacheProvider;
 use DataKit\DataViews\Data\ArrayDataSource;
 use DataKit\DataViews\Data\CachedDataSource;
@@ -91,8 +92,26 @@ public function test_caching(): void {
 		// Get fields is always piped through.
 		self::assertCount( 6, $this->trace->get_calls() );
 
+		$ds_2 = new CachedDataSource(
+			new ArrayDataSource( 'second-source', [ 'three' => [ 'name' => 'Person 3' ] ] ),
+			$cache
+		);
+
+		// Helper method to inspect the private $items variable.
+		$get_items_count = Closure::fromCallable( function () {
+			return count( $this->items ); // @phpstan-ignore property.notFound
+		} )->bindTo( $cache, $cache );
+
+		// Trigger caching for second data source.
+		self::assertSame( [ 'three' ], $ds_2->get_data_ids() );
+		self::assertSame( 2, $get_items_count() );
+		// Clear cache for this data source only.
 		$ds->clear_cache();
+
+		self::assertSame( 1, $get_items_count() );
 		$ds->get_data_ids();
+
+		self::assertSame( 2, $get_items_count() );
 		// Cache cleared.
 		self::assertCount( 7, $this->trace->get_calls() );
 	}
@@ -153,7 +172,17 @@ public function testCount(): void {
 		self::assertCount( 2, $ds );
 		self::assertSame( 2, $ds->count() ); // second call
 
-		self::assertCount( 1, $this->trace->get_calls() );
+		$asc_sort = $ds->sort_by( Sort::asc( 'name' ) );
+		self::assertSame( 2, $asc_sort->count() );
+
+		$desc_sort = $ds->sort_by( Sort::desc( 'name' ) );
+		self::assertSame( 2, $desc_sort->count() );
+
+		// Count should be called only once on the trace, as the sorting does not influence the cache key.
+		self::assertSame(
+			[ 'count', 'sort_by', 'sort_by' ],
+			array_column( $this->trace->get_calls(), 0 )
+		);
 	}
 
 	/**
diff --git a/tests/Data/TraceableDataSource.php b/tests/Data/TraceableDataSource.php
index 654324b..614a484 100644
--- a/tests/Data/TraceableDataSource.php
+++ b/tests/Data/TraceableDataSource.php
@@ -16,7 +16,6 @@
  * @since $ver$
  */
 final class TraceableDataSource implements MutableDataSource {
-
 	/**
 	 * The decorated data source.
 	 *
@@ -59,7 +58,7 @@ public function id() : string {
 	 * @since $ver$
 	 */
 	public function get_data_by_id( string $id ) : array {
-		$this->calls[] = [ __METHOD__, ...func_get_args() ];
+		$this->calls[] = [ __FUNCTION__, ...func_get_args() ];
 
 		return $this->inner->get_data_by_id( $id );
 	}
@@ -69,7 +68,7 @@ public function get_data_by_id( string $id ) : array {
 	 * @since $ver$
 	 */
 	public function get_fields() : array {
-		$this->calls[] = [ __METHOD__ ];
+		$this->calls[] = [ __FUNCTION__ ];
 
 		return $this->inner->get_fields();
 	}
@@ -79,7 +78,7 @@ public function get_fields() : array {
 	 * @since $ver$
 	 */
 	public function get_data_ids( int $limit = 20, int $offset = 0 ) : array {
-		$this->calls[] = [ __METHOD__, ...func_get_args() ];
+		$this->calls[] = [ __FUNCTION__, ...func_get_args() ];
 
 		return $this->inner->get_data_ids( $limit, $offset );
 	}
@@ -89,7 +88,7 @@ public function get_data_ids( int $limit = 20, int $offset = 0 ) : array {
 	 * @since $ver$
 	 */
 	public function filter_by( ?Filters $filters ) : self {
-		$this->calls[] = [ __METHOD__, ...func_get_args() ];
+		$this->calls[] = [ __FUNCTION__, ...func_get_args() ];
 
 		$this->inner = $this->inner->filter_by( $filters );
 
@@ -101,7 +100,7 @@ public function filter_by( ?Filters $filters ) : self {
 	 * @since $ver$
 	 */
 	public function sort_by( ?Sort $sort ) : self {
-		$this->calls[] = [ __METHOD__, ...func_get_args() ];
+		$this->calls[] = [ __FUNCTION__, ...func_get_args() ];
 
 		$this->inner = $this->inner->sort_by( $sort );
 
@@ -113,7 +112,7 @@ public function sort_by( ?Sort $sort ) : self {
 	 * @since $ver$
 	 */
 	public function search_by( ?Search $search ) : self {
-		$this->calls[] = [ __METHOD__, ...func_get_args() ];
+		$this->calls[] = [ __FUNCTION__, ...func_get_args() ];
 		$this->inner   = $this->inner->search_by( $search );
 
 		return $this;
@@ -143,7 +142,7 @@ public function reset() : void {
 	 * @since $ver$
 	 */
 	public function count() : int {
-		$this->calls[] = [ __METHOD__ ];
+		$this->calls[] = [ __FUNCTION__ ];
 
 		return $this->inner->count();
 	}
@@ -156,7 +155,7 @@ public function can_delete() : bool {
 		if ( ! $this->inner instanceof MutableDataSource ) {
 			return false;
 		}
-		$this->calls[] = [ __METHOD__ ];
+		$this->calls[] = [ __FUNCTION__ ];
 
 		return $this->inner->can_delete();
 	}
@@ -170,7 +169,7 @@ public function delete_data_by_id( string ...$ids ) : void {
 			return;
 		}
 
-		$this->calls[] = [ __METHOD__ ];
+		$this->calls[] = [ __FUNCTION__ ];
 
 		$this->inner->delete_data_by_id( ...$ids );
 	}