diff --git a/lib/Database.php b/lib/Database.php
index 7c47ad3..cecfb33 100644
--- a/lib/Database.php
+++ b/lib/Database.php
@@ -37,7 +37,7 @@ use JKingWeb\Arsse\Misc\ValueInfo;
  */
 class Database {
     /** The version number of the latest schema the interface is aware of */
-    const SCHEMA_VERSION = 4;
+    const SCHEMA_VERSION = 5;
     /** The size of a set of values beyond which the set will be embedded into the query text */
     const LIMIT_SET_SIZE = 25;
     /** The length of a string in an embedded set beyond which a parameter placeholder will be used for the string */
diff --git a/sql/MySQL/0.sql b/sql/MySQL/0.sql
index f6b00e2..3901ad7 100644
--- a/sql/MySQL/0.sql
+++ b/sql/MySQL/0.sql
@@ -5,7 +5,7 @@
 -- Please consult the SQLite 3 schemata for commented version
 
 create table arsse_meta(
-    `key` varchar(255) primary key,
+    "key" varchar(255) primary key,
     value longtext
 ) character set utf8mb4;
 
@@ -21,9 +21,9 @@ create table arsse_users(
 
 create table arsse_users_meta(
     owner varchar(255) not null references arsse_users(id) on delete cascade on update cascade,
-    `key` varchar(255) not null,
+    "key" varchar(255) not null,
     value varchar(255),
-    primary key(owner,`key`)
+    primary key(owner,"key")
 ) character set utf8mb4;
 
 create table arsse_folders(
@@ -93,7 +93,7 @@ create table arsse_enclosures(
 create table arsse_marks(
     article bigint not null references arsse_articles(id) on delete cascade,
     subscription bigint not null references arsse_subscriptions(id) on delete cascade on update cascade,
-    `read` boolean not null default 0,
+    "read" boolean not null default 0,
     starred boolean not null default 0,
     modified datetime(0) not null default CURRENT_TIMESTAMP,
     primary key(article,subscription)
@@ -110,4 +110,4 @@ create table arsse_categories(
     name varchar(255)
 ) character set utf8mb4;
 
-insert into arsse_meta(`key`,value) values('schema_version','1');
+insert into arsse_meta("key",value) values('schema_version','1');
diff --git a/sql/MySQL/1.sql b/sql/MySQL/1.sql
index eb4ce5f..f7a8542 100644
--- a/sql/MySQL/1.sql
+++ b/sql/MySQL/1.sql
@@ -8,7 +8,7 @@ create table arsse_sessions (
     id varchar(255) primary key,
     created datetime(0) not null default CURRENT_TIMESTAMP,
     expires datetime(0) not null,
-    `user` varchar(255) not null references arsse_users(id) on delete cascade on update cascade
+    "user" varchar(255) not null references arsse_users(id) on delete cascade on update cascade
 ) character set utf8mb4;
 
 create table arsse_labels (
@@ -30,4 +30,4 @@ create table arsse_label_members (
 
 alter table arsse_marks add column note longtext;
 
-update arsse_meta set value = '2' where `key` = 'schema_version';
+update arsse_meta set value = '2' where "key" = 'schema_version';
diff --git a/sql/MySQL/2.sql b/sql/MySQL/2.sql
index d63cbb6..feaf4c9 100644
--- a/sql/MySQL/2.sql
+++ b/sql/MySQL/2.sql
@@ -20,4 +20,4 @@ alter table arsse_articles convert to character set utf8mb4 collate utf8mb4_unic
 alter table arsse_categories convert to character set utf8mb4 collate utf8mb4_unicode_ci;
 alter table arsse_labels convert to character set utf8mb4 collate utf8mb4_unicode_ci;
 
-update arsse_meta set value = '3' where `key` = 'schema_version';
+update arsse_meta set value = '3' where "key" = 'schema_version';
diff --git a/sql/MySQL/3.sql b/sql/MySQL/3.sql
index c02df03..32f87a6 100644
--- a/sql/MySQL/3.sql
+++ b/sql/MySQL/3.sql
@@ -7,4 +7,4 @@
 alter table arsse_marks change column modified modified datetime(0);
 alter table arsse_marks add column touched boolean not null default 0;
 
-update arsse_meta set value = '4' where `key` = 'schema_version';
+update arsse_meta set value = '4' where "key" = 'schema_version';
diff --git a/sql/MySQL/4.sql b/sql/MySQL/4.sql
new file mode 100644
index 0000000..aa073a6
--- /dev/null
+++ b/sql/MySQL/4.sql
@@ -0,0 +1,23 @@
+-- SPDX-License-Identifier: MIT
+-- Copyright 2017 J. King, Dustin Wilson et al.
+-- See LICENSE and AUTHORS files for details
+
+-- Please consult the SQLite 3 schemata for commented version
+
+create table arsse_tags(
+    id serial primary key,
+    owner varchar(255) not null references arsse_users(id) on delete cascade on update cascade,
+    name varchar(255) not null,
+    modified datetime(0) not null default CURRENT_TIMESTAMP,
+    unique(owner,name)
+) character set utf8mb4 collate utf8mb4_unicode_ci;
+
+create table arsse_tag_members(
+    tag bigint not null references arsse_tags(id) on delete cascade,
+    subscription bigint not null references arsse_subscriptions(id) on delete cascade,
+    assigned boolean not null default 1,
+    modified datetime(0) not null default CURRENT_TIMESTAMP,
+    primary key(tag,subscription)
+) character set utf8mb4 collate utf8mb4_unicode_ci;
+
+update arsse_meta set value = '5' where "key" = 'schema_version';
diff --git a/sql/PostgreSQL/0.sql b/sql/PostgreSQL/0.sql
index 3d940f5..d11c2c4 100644
--- a/sql/PostgreSQL/0.sql
+++ b/sql/PostgreSQL/0.sql
@@ -110,4 +110,4 @@ create table arsse_categories(
     name text
 );
 
-insert into arsse_meta(key,value) values('schema_version','1');
+insert into arsse_meta("key",value) values('schema_version','1');
diff --git a/sql/PostgreSQL/1.sql b/sql/PostgreSQL/1.sql
index 1549fd5..d2a5480 100644
--- a/sql/PostgreSQL/1.sql
+++ b/sql/PostgreSQL/1.sql
@@ -30,4 +30,4 @@ create table arsse_label_members (
 
 alter table arsse_marks add column note text not null default '';
 
-update arsse_meta set value = '2' where key = 'schema_version';
+update arsse_meta set value = '2' where "key" = 'schema_version';
diff --git a/sql/PostgreSQL/2.sql b/sql/PostgreSQL/2.sql
index 847edb7..33863fb 100644
--- a/sql/PostgreSQL/2.sql
+++ b/sql/PostgreSQL/2.sql
@@ -13,4 +13,4 @@ alter table arsse_articles alter column author type text collate "und-x-icu";
 alter table arsse_categories alter column name type text collate "und-x-icu";
 alter table arsse_labels alter column name type text collate "und-x-icu";
 
-update arsse_meta set value = '3' where key = 'schema_version';
+update arsse_meta set value = '3' where "key" = 'schema_version';
diff --git a/sql/PostgreSQL/3.sql b/sql/PostgreSQL/3.sql
index 2290ae5..091cf46 100644
--- a/sql/PostgreSQL/3.sql
+++ b/sql/PostgreSQL/3.sql
@@ -8,4 +8,4 @@ alter table arsse_marks alter column modified drop default;
 alter table arsse_marks alter column modified drop not null;
 alter table arsse_marks add column touched smallint not null default 0;
 
-update arsse_meta set value = '4' where key = 'schema_version';
+update arsse_meta set value = '4' where "key" = 'schema_version';
diff --git a/sql/PostgreSQL/4.sql b/sql/PostgreSQL/4.sql
new file mode 100644
index 0000000..e0cd8eb
--- /dev/null
+++ b/sql/PostgreSQL/4.sql
@@ -0,0 +1,23 @@
+-- SPDX-License-Identifier: MIT
+-- Copyright 2017 J. King, Dustin Wilson et al.
+-- See LICENSE and AUTHORS files for details
+
+-- Please consult the SQLite 3 schemata for commented version
+
+create table arsse_tags(
+    id bigserial primary key,
+    owner text not null references arsse_users(id) on delete cascade on update cascade,
+    name text not null collate "und-x-icu",
+    modified timestamp(0) without time zone not null default CURRENT_TIMESTAMP,
+    unique(owner,name)
+);
+
+create table arsse_tag_members(
+    tag bigint not null references arsse_tags(id) on delete cascade,
+    subscription bigint not null references arsse_subscriptions(id) on delete cascade,
+    assigned smallint not null default 1,
+    modified timestamp(0) without time zone not null default CURRENT_TIMESTAMP,
+    primary key(tag,subscription)
+);
+
+update arsse_meta set value = '5' where "key" = 'schema_version';
diff --git a/sql/SQLite3/0.sql b/sql/SQLite3/0.sql
index 7a9dea6..97f5451 100644
--- a/sql/SQLite3/0.sql
+++ b/sql/SQLite3/0.sql
@@ -130,4 +130,4 @@ create table arsse_categories(
 
 -- set version marker
 pragma user_version = 1;
-insert into arsse_meta(key,value) values('schema_version','1');
+insert into arsse_meta("key",value) values('schema_version','1');
diff --git a/sql/SQLite3/1.sql b/sql/SQLite3/1.sql
index dc7862d..3817645 100644
--- a/sql/SQLite3/1.sql
+++ b/sql/SQLite3/1.sql
@@ -20,7 +20,7 @@ create table arsse_labels(
 );
 
 create table arsse_label_members(
--- uabels assignments for articles
+-- label assignments for articles
     label integer not null references arsse_labels(id) on delete cascade,                   -- label ID associated to an article; label IDs belong to a user
     article integer not null references arsse_articles(id) on delete cascade,               -- article associated to a label
     subscription integer not null references arsse_subscriptions(id) on delete cascade,     -- Subscription is included so that records are deleted when a subscription is removed
@@ -48,4 +48,4 @@ alter table arsse_marks_new rename to arsse_marks;
 
 -- set version marker
 pragma user_version = 2;
-update arsse_meta set value = '2' where key = 'schema_version';
+update arsse_meta set value = '2' where "key" = 'schema_version';
diff --git a/sql/SQLite3/2.sql b/sql/SQLite3/2.sql
index b378467..14a253d 100644
--- a/sql/SQLite3/2.sql
+++ b/sql/SQLite3/2.sql
@@ -121,4 +121,4 @@ alter table arsse_labels_new rename to arsse_labels;
 
 -- set version marker
 pragma user_version = 3;
-update arsse_meta set value = '3' where key = 'schema_version';
+update arsse_meta set value = '3' where "key" = 'schema_version';
diff --git a/sql/SQLite3/3.sql b/sql/SQLite3/3.sql
index 0d58324..087bf32 100644
--- a/sql/SQLite3/3.sql
+++ b/sql/SQLite3/3.sql
@@ -24,4 +24,4 @@ reindex nocase;
 
 -- set version marker
 pragma user_version = 4;
-update arsse_meta set value = '4' where key = 'schema_version';
+update arsse_meta set value = '4' where "key" = 'schema_version';
diff --git a/sql/SQLite3/4.sql b/sql/SQLite3/4.sql
new file mode 100644
index 0000000..aa7cfbd
--- /dev/null
+++ b/sql/SQLite3/4.sql
@@ -0,0 +1,25 @@
+-- SPDX-License-Identifier: MIT
+-- Copyright 2017 J. King, Dustin Wilson et al.
+-- See LICENSE and AUTHORS files for details
+
+create table arsse_tags(
+-- user-defined subscription tags
+    id integer primary key,                                                                 -- numeric ID
+    owner text not null references arsse_users(id) on delete cascade on update cascade,     -- owning user
+    name text not null collate nocase,                                                      -- tag text
+    modified text not null default CURRENT_TIMESTAMP,                                       -- time at which the tag was last modified
+    unique(owner,name)
+);
+
+create table arsse_tag_members(
+-- tag assignments for subscriptions
+    tag integer not null references arsse_tags(id) on delete cascade,                       -- tag ID associated to a subscription
+    subscription integer not null references arsse_subscriptions(id) on delete cascade,     -- Subscription associated to a tag
+    assigned boolean not null default 1,                                                    -- whether the association is current, to support soft deletion
+    modified text not null default CURRENT_TIMESTAMP,                                       -- time at which the association was last made or unmade
+    primary key(tag,subscription)                                                           -- only one association of a given tag to a given subscription
+) without rowid;
+
+-- set version marker
+pragma user_version = 5;
+update arsse_meta set value = '5' where "key" = 'schema_version';