diff --git a/examples/axum-app/app/Cargo.toml b/examples/axum-app/app/Cargo.toml
index caac386..b046f31 100644
--- a/examples/axum-app/app/Cargo.toml
+++ b/examples/axum-app/app/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "axum-app"
-version = "0.3.1"
+version = "0.4.0"
 rust-version = "1.68"
 edition = "2021"
 publish = false
@@ -12,13 +12,9 @@ tracing = { version = "0.1.37" }
 
 [dependencies.zino]
 path = "../../../zino"
-version = "0.3.1"
-features = ["axum-server"]
-
-[dependencies.zino-core]
-path = "../../../zino-core"
-version = "0.3.1"
+version = "0.4.0"
+features = ["axum"]
 
 [dependencies.zino-model]
 path = "../../../zino-model"
-version = "0.3.1"
+version = "0.3.2"
diff --git a/examples/axum-app/app/src/controller/stats.rs b/examples/axum-app/app/src/controller/stats.rs
index 10ac619..9ee9423 100644
--- a/examples/axum-app/app/src/controller/stats.rs
+++ b/examples/axum-app/app/src/controller/stats.rs
@@ -1,6 +1,5 @@
 use serde_json::json;
-use zino::Request;
-use zino_core::{RequestContext, Response};
+use zino::{Request, RequestContext, Response};
 
 pub(crate) async fn index(req: Request) -> zino::Result {
     let mut res = Response::default();
diff --git a/examples/axum-app/app/src/controller/user.rs b/examples/axum-app/app/src/controller/user.rs
index a80f321..8fa0dc7 100644
--- a/examples/axum-app/app/src/controller/user.rs
+++ b/examples/axum-app/app/src/controller/user.rs
@@ -1,6 +1,8 @@
 use serde_json::json;
-use zino::{AxumCluster, Request};
-use zino_core::{Application, Model, Query, Rejection, RequestContext, Response, Schema, Uuid};
+use zino::{
+    Application, AxumCluster, Model, Query, Rejection, Request, RequestContext, Response, Schema,
+    Uuid,
+};
 use zino_model::User;
 
 pub(crate) async fn new(mut req: Request) -> zino::Result {
diff --git a/examples/axum-app/app/src/main.rs b/examples/axum-app/app/src/main.rs
index 9ea3bfb..c729411 100644
--- a/examples/axum-app/app/src/main.rs
+++ b/examples/axum-app/app/src/main.rs
@@ -2,7 +2,7 @@ mod controller;
 mod router;
 mod schedule;
 
-use zino_core::Application;
+use zino::Application;
 
 fn main() {
     zino::AxumCluster::new()
diff --git a/examples/axum-app/app/src/schedule/job.rs b/examples/axum-app/app/src/schedule/job.rs
index c064ac0..0f8d9fb 100644
--- a/examples/axum-app/app/src/schedule/job.rs
+++ b/examples/axum-app/app/src/schedule/job.rs
@@ -1,4 +1,4 @@
-use zino_core::{BoxFuture, DateTime, Map, Query, Schema, Uuid};
+use zino::{BoxFuture, DateTime, Map, Query, Schema, Uuid};
 use zino_model::User;
 
 pub(super) fn every_15s(job_id: Uuid, job_data: &mut Map, _last_tick: DateTime) {
diff --git a/examples/axum-app/app/src/schedule/mod.rs b/examples/axum-app/app/src/schedule/mod.rs
index c2165c1..9d9ad9f 100644
--- a/examples/axum-app/app/src/schedule/mod.rs
+++ b/examples/axum-app/app/src/schedule/mod.rs
@@ -1,5 +1,5 @@
 use std::collections::HashMap;
-use zino_core::{AsyncCronJob, CronJob};
+use zino::{AsyncCronJob, CronJob};
 
 mod job;
 
diff --git a/examples/axum-app/config/config.dev.toml b/examples/axum-app/config/config.dev.toml
index 72d1601..bf1e5c8 100644
--- a/examples/axum-app/config/config.dev.toml
+++ b/examples/axum-app/config/config.dev.toml
@@ -1,6 +1,6 @@
 
 name = "data-cube"
-version = "0.3.1"
+version = "0.4.0"
 
 [main]
 host = "127.0.0.1"
diff --git a/examples/axum-app/config/config.prod.toml b/examples/axum-app/config/config.prod.toml
index d766aaf..932e56e 100644
--- a/examples/axum-app/config/config.prod.toml
+++ b/examples/axum-app/config/config.prod.toml
@@ -1,6 +1,6 @@
 
 name = "data-cube"
-version = "0.3.1"
+version = "0.4.0"
 
 [main]
 host = "127.0.0.1"
@@ -27,7 +27,7 @@ username = "postgres"
 password = "G76hTg8T5Aa+SZQFc+0QnsRLo1UOjqpkp/jUQ+lySc8QCt4B"
 
 [tracing]
-filter = "info,sqlx=warn"
+filter = "info,sqlx=warn,tower_http=warn"
 
 [metrics]
 exporter = "prometheus"
diff --git a/zino-core/Cargo.toml b/zino-core/Cargo.toml
index aec58ca..7e76bc4 100644
--- a/zino-core/Cargo.toml
+++ b/zino-core/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "zino-core"
 description = "Core types and traits for zino."
-version = "0.3.1"
+version = "0.4.0"
 rust-version = "1.68"
 edition = "2021"
 license = "MIT"
diff --git a/zino-core/src/application.rs b/zino-core/src/application.rs
index 570472f..fe9f488 100644
--- a/zino-core/src/application.rs
+++ b/zino-core/src/application.rs
@@ -1,4 +1,10 @@
-use crate::{AsyncCronJob, CronJob, Job, JobScheduler, Map, State};
+//! Application trait.
+
+use crate::{
+    schedule::{AsyncCronJob, CronJob, Job, JobScheduler},
+    state::State,
+    Map,
+};
 use metrics_exporter_prometheus::{Matcher, PrometheusBuilder};
 use metrics_exporter_tcp::TcpBuilder;
 use std::{
diff --git a/zino-core/src/authentication/mod.rs b/zino-core/src/authentication/mod.rs
index 3ecc361..5c1c192 100644
--- a/zino-core/src/authentication/mod.rs
+++ b/zino-core/src/authentication/mod.rs
@@ -1,4 +1,6 @@
-use crate::{DateTime, Map, Validation};
+//! Access keys and security tokens.
+
+use crate::{datetime::DateTime, request::Validation, Map};
 use hmac::{
     digest::{FixedOutput, KeyInit, MacMarker, Update},
     Mac,
@@ -8,9 +10,8 @@ use std::time::Duration;
 mod access_key;
 mod security_token;
 
-// Rexports.
 pub use access_key::{AccessKeyId, SecretAccessKey};
-pub(crate) use security_token::ParseTokenError;
+pub(super) use security_token::ParseTokenError;
 pub use security_token::SecurityToken;
 
 /// HTTP signature using HMAC.
diff --git a/zino-core/src/authentication/security_token.rs b/zino-core/src/authentication/security_token.rs
index 0f4a063..ce31b71 100644
--- a/zino-core/src/authentication/security_token.rs
+++ b/zino-core/src/authentication/security_token.rs
@@ -1,4 +1,4 @@
-use crate::{crypto, AccessKeyId, DateTime};
+use crate::{authentication::AccessKeyId, crypto, datetime::DateTime};
 use std::fmt;
 
 /// An error which can be returned when parsing a token.
diff --git a/zino-core/src/cache.rs b/zino-core/src/cache.rs
index 2722b6a..a9bf70c 100644
--- a/zino-core/src/cache.rs
+++ b/zino-core/src/cache.rs
@@ -1,10 +1,11 @@
+//! Global cache for the application.
+
 use lru::LruCache;
 use parking_lot::RwLock;
 use serde_json::Value;
 use std::{num::NonZeroUsize, sync::LazyLock};
 
-/// Global cache for the application.
-/// See the docs for [LruCache](https://docs.rs/lru/latest/lru/struct.LruCache.html).
+/// Global cache based on [LruCache](https://docs.rs/lru/latest/lru/struct.LruCache.html).
 #[derive(Debug, Clone, Copy, Default)]
 pub struct GlobalCache;
 
diff --git a/zino-core/src/channel/cloud_event.rs b/zino-core/src/channel/cloud_event.rs
index 63280e9..df29679 100644
--- a/zino-core/src/channel/cloud_event.rs
+++ b/zino-core/src/channel/cloud_event.rs
@@ -1,4 +1,4 @@
-use crate::{DateTime, Map};
+use crate::{datetime::DateTime, Map};
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
 
diff --git a/zino-core/src/channel/mod.rs b/zino-core/src/channel/mod.rs
index d94f6c0..800c9a6 100644
--- a/zino-core/src/channel/mod.rs
+++ b/zino-core/src/channel/mod.rs
@@ -1,6 +1,7 @@
+//! Cloud events and subscriptions.
+
 mod cloud_event;
 mod subscription;
 
-// Reexports.
 pub use cloud_event::CloudEvent;
 pub use subscription::Subscription;
diff --git a/zino-core/src/database/mod.rs b/zino-core/src/database/mod.rs
index 78aef9c..5cf0c9b 100644
--- a/zino-core/src/database/mod.rs
+++ b/zino-core/src/database/mod.rs
@@ -1,3 +1,5 @@
+//! Connection pool and ORM.
+
 use crate::{crypto, state::SHARED_STATE};
 use sqlx::{
     postgres::{PgConnectOptions, PgPoolOptions},
@@ -12,7 +14,6 @@ mod mutation;
 mod query;
 mod schema;
 
-// Reexports.
 pub use column::Column;
 pub use model::Model;
 pub use mutation::Mutation;
diff --git a/zino-core/src/database/model.rs b/zino-core/src/database/model.rs
index 9b64d7a..b8d9bfb 100644
--- a/zino-core/src/database/model.rs
+++ b/zino-core/src/database/model.rs
@@ -1,4 +1,4 @@
-use crate::{Map, Validation};
+use crate::{request::Validation, Map};
 use serde::{de::DeserializeOwned, Serialize};
 use serde_json::{Error, Value};
 
diff --git a/zino-core/src/database/mutation.rs b/zino-core/src/database/mutation.rs
index 03e3aa2..cb1d15c 100644
--- a/zino-core/src/database/mutation.rs
+++ b/zino-core/src/database/mutation.rs
@@ -1,4 +1,4 @@
-use crate::{Map, Schema, Validation};
+use crate::{database::Schema, request::Validation, Map};
 
 #[derive(Debug, Clone, Default)]
 /// SQL mutation builder.
diff --git a/zino-core/src/database/query.rs b/zino-core/src/database/query.rs
index 6e0950d..ad4cf9b 100644
--- a/zino-core/src/database/query.rs
+++ b/zino-core/src/database/query.rs
@@ -1,4 +1,8 @@
-use crate::{Column, Map, Schema, Validation};
+use crate::{
+    database::{Column, Schema},
+    request::Validation,
+    Map,
+};
 use serde_json::Value;
 
 #[derive(Debug, Clone, Default)]
diff --git a/zino-core/src/database/schema.rs b/zino-core/src/database/schema.rs
index 6ada567..ffe326b 100644
--- a/zino-core/src/database/schema.rs
+++ b/zino-core/src/database/schema.rs
@@ -1,4 +1,8 @@
-use crate::{Column, ConnectionPool, Map, Model, Mutation, Query, Validation};
+use crate::{
+    database::{Column, ConnectionPool, Model, Mutation, Query},
+    request::Validation,
+    Map,
+};
 use futures::TryStreamExt;
 use serde::de::DeserializeOwned;
 use serde_json::json;
diff --git a/zino-core/src/datetime.rs b/zino-core/src/datetime.rs
index 387e1ff..484e01d 100644
--- a/zino-core/src/datetime.rs
+++ b/zino-core/src/datetime.rs
@@ -1,3 +1,5 @@
+//! ISO 8601 combined date and time with local time zone.
+
 use chrono::{
     format::{ParseError, ParseResult},
     Local, NaiveDateTime, SecondsFormat, TimeZone, Utc,
@@ -11,7 +13,7 @@ use std::{
     time::Duration,
 };
 
-/// ISO 8601 combined date and time with local time zone.
+/// A wrapper type for `chrono::DateTime<Local>`.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Serialize, Deserialize)]
 pub struct DateTime(chrono::DateTime<Local>);
 
diff --git a/zino-core/src/lib.rs b/zino-core/src/lib.rs
index 7b3c926..ac6e27d 100644
--- a/zino-core/src/lib.rs
+++ b/zino-core/src/lib.rs
@@ -11,29 +11,17 @@
 #![feature(type_alias_impl_trait)]
 #![forbid(unsafe_code)]
 
-mod application;
-mod authentication;
-mod cache;
-mod channel;
-mod crypto;
-mod database;
-mod datetime;
-mod request;
-mod response;
-mod schedule;
-mod state;
-
-// Reexports.
-pub use application::Application;
-pub use authentication::{AccessKeyId, Authentication, SecretAccessKey, SecurityToken};
-pub use cache::GlobalCache;
-pub use channel::{CloudEvent, Subscription};
-pub use database::{Column, ConnectionPool, Model, Mutation, Query, Schema};
-pub use datetime::DateTime;
-pub use request::{Context, RequestContext, Validation};
-pub use response::{Rejection, Response, ResponseCode};
-pub use schedule::{AsyncCronJob, CronJob, Job, JobScheduler};
-pub use state::State;
+pub mod application;
+pub mod authentication;
+pub mod cache;
+pub mod channel;
+pub mod crypto;
+pub mod database;
+pub mod datetime;
+pub mod request;
+pub mod response;
+pub mod schedule;
+pub mod state;
 
 /// A JSON key/value type.
 pub type Map = serde_json::Map<String, serde_json::Value>;
diff --git a/zino-core/src/request/mod.rs b/zino-core/src/request/mod.rs
index 1a971d5..ea53c1a 100644
--- a/zino-core/src/request/mod.rs
+++ b/zino-core/src/request/mod.rs
@@ -1,6 +1,12 @@
+//! Request context and validation.
+
 use crate::{
-    authentication::ParseTokenError, Authentication, CloudEvent, DateTime, Map, Model, Query,
-    Rejection, Response, ResponseCode, SecurityToken, Subscription, Uuid,
+    authentication::{Authentication, ParseTokenError, SecurityToken},
+    channel::{CloudEvent, Subscription},
+    database::{Model, Query},
+    datetime::DateTime,
+    response::{Rejection, Response, ResponseCode},
+    Map, Uuid,
 };
 use http::uri::Uri;
 use http_types::{trace::TraceContext, Trailers};
@@ -13,7 +19,6 @@ use toml::value::Table;
 mod context;
 mod validation;
 
-// Reexports.
 pub use context::Context;
 pub use validation::Validation;
 
diff --git a/zino-core/src/request/validation.rs b/zino-core/src/request/validation.rs
index 1f78bc9..69f2cf4 100644
--- a/zino-core/src/request/validation.rs
+++ b/zino-core/src/request/validation.rs
@@ -1,4 +1,4 @@
-use crate::{DateTime, Map, Response};
+use crate::{datetime::DateTime, response::Response, Map};
 use bytes::Bytes;
 use http_body::Full;
 use serde_json::Value;
diff --git a/zino-core/src/response/mod.rs b/zino-core/src/response/mod.rs
index be1b0bf..3956c62 100644
--- a/zino-core/src/response/mod.rs
+++ b/zino-core/src/response/mod.rs
@@ -1,4 +1,9 @@
-use crate::{RequestContext, SharedString, Uuid, Validation};
+//! Constructing responses and rejections.
+
+use crate::{
+    request::{RequestContext, Validation},
+    SharedString, Uuid,
+};
 use bytes::Bytes;
 use http::header::{self, HeaderValue};
 use http_body::Full;
@@ -13,7 +18,6 @@ use std::{
 
 mod rejection;
 
-// Reexports.
 pub use rejection::Rejection;
 
 /// Response code.
diff --git a/zino-core/src/response/rejection.rs b/zino-core/src/response/rejection.rs
index 64ee803..1330561 100644
--- a/zino-core/src/response/rejection.rs
+++ b/zino-core/src/response/rejection.rs
@@ -1,4 +1,4 @@
-use crate::{BoxError, Response, Validation};
+use crate::{request::Validation, response::Response, BoxError};
 use bytes::Bytes;
 use http_body::Full;
 use std::{error, fmt};
diff --git a/zino-core/src/schedule/mod.rs b/zino-core/src/schedule/mod.rs
index 4c053da..efb85d2 100644
--- a/zino-core/src/schedule/mod.rs
+++ b/zino-core/src/schedule/mod.rs
@@ -1,4 +1,6 @@
-use crate::{BoxFuture, DateTime, Map, Uuid};
+//! Scheduler for sync and async cron jobs.
+
+use crate::{datetime::DateTime, BoxFuture, Map, Uuid};
 use chrono::Local;
 use cron::Schedule;
 use std::{str::FromStr, time::Duration};
diff --git a/zino-core/src/state.rs b/zino-core/src/state.rs
index f29b6f4..b12cfc2 100644
--- a/zino-core/src/state.rs
+++ b/zino-core/src/state.rs
@@ -1,3 +1,5 @@
+//! Application state.
+
 use crate::Map;
 use std::{
     env, fs,
diff --git a/zino-derive/Cargo.toml b/zino-derive/Cargo.toml
index e51d6ee..45811f2 100644
--- a/zino-derive/Cargo.toml
+++ b/zino-derive/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "zino-derive"
 description = "Derived traits for zino."
-version = "0.3.1"
+version = "0.3.2"
 rust-version = "1.68"
 edition = "2021"
 license = "MIT"
@@ -20,4 +20,4 @@ syn = { version = "1.0.107", features = ["full", "extra-traits"] }
 
 [dependencies.zino-core]
 path = "../zino-core"
-version = "0.3.1"
+version = "0.4.0"
diff --git a/zino-derive/src/lib.rs b/zino-derive/src/lib.rs
index 8469f98..e37ad28 100644
--- a/zino-derive/src/lib.rs
+++ b/zino-derive/src/lib.rs
@@ -99,7 +99,7 @@ pub fn schema_macro(item: TokenStream) -> TokenStream {
                     None => quote! { None },
                 };
                 let column = quote! {
-                    zino_core::Column::new(#name, #type_name, #quote_value, #not_null, #quote_index)
+                    zino_core::database::Column::new(#name, #type_name, #quote_value, #not_null, #quote_index)
                 };
                 columns.push(column);
             }
@@ -114,14 +114,15 @@ pub fn schema_macro(item: TokenStream) -> TokenStream {
     let columns_len = columns.len();
     let output = quote! {
         use std::sync::{LazyLock, OnceLock};
+        use zino_core::database::{Column, ConnectionPool, Schema};
 
-        static #schema_columns: LazyLock<[zino_core::Column; #columns_len]> = LazyLock::new(|| {
+        static #schema_columns: LazyLock<[Column; #columns_len]> = LazyLock::new(|| {
             [#(#columns),*]
         });
-        static #schema_reader: OnceLock<&zino_core::ConnectionPool> = OnceLock::new();
-        static #schema_writer: OnceLock<&zino_core::ConnectionPool> = OnceLock::new();
+        static #schema_reader: OnceLock<&ConnectionPool> = OnceLock::new();
+        static #schema_writer: OnceLock<&ConnectionPool> = OnceLock::new();
 
-        impl zino_core::Schema for #name {
+        impl Schema for #name {
             /// Type name as a str.
             const TYPE_NAME: &'static str = #type_name_lowercase;
             /// Primary key name as a str.
@@ -133,8 +134,8 @@ pub fn schema_macro(item: TokenStream) -> TokenStream {
 
             /// Returns a reference to the columns.
             #[inline]
-            fn columns() -> &'static [zino_core::Column<'static>] {
-                std::sync::LazyLock::force(&#schema_columns).as_slice()
+            fn columns() -> &'static [Column<'static>] {
+                LazyLock::force(&#schema_columns).as_slice()
             }
 
             /// Returns the primary key value as a `String`.
@@ -144,7 +145,7 @@ pub fn schema_macro(item: TokenStream) -> TokenStream {
             }
 
             /// Gets the model reader.
-            async fn get_reader() -> Option<&'static zino_core::ConnectionPool> {
+            async fn get_reader() -> Option<&'static ConnectionPool> {
                 match #schema_reader.get() {
                     Some(connection_pool) => Some(*connection_pool),
                     None => {
@@ -158,7 +159,7 @@ pub fn schema_macro(item: TokenStream) -> TokenStream {
             }
 
             /// Gets the model writer.
-            async fn get_writer() -> Option<&'static zino_core::ConnectionPool> {
+            async fn get_writer() -> Option<&'static ConnectionPool> {
                 match #schema_writer.get() {
                     Some(connection_pool) => Some(*connection_pool),
                     None => {
@@ -172,14 +173,14 @@ pub fn schema_macro(item: TokenStream) -> TokenStream {
             }
         }
 
-        impl std::cmp::PartialEq for #name {
+        impl PartialEq for #name {
             #[inline]
             fn eq(&self, other: &Self) -> bool {
                 self.#schema_primary_key == other.#schema_primary_key
             }
         }
 
-        impl std::cmp::Eq for #name {}
+        impl Eq for #name {}
     };
 
     TokenStream::from(output)
diff --git a/zino-model/Cargo.toml b/zino-model/Cargo.toml
index aa5dca2..893e82f 100644
--- a/zino-model/Cargo.toml
+++ b/zino-model/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "zino-model"
 description = "Model types for zino."
-version = "0.3.1"
+version = "0.3.2"
 rust-version = "1.68"
 edition = "2021"
 license = "MIT"
@@ -15,8 +15,8 @@ serde = { version = "1.0.152", features = ["derive"] }
 
 [dependencies.zino-core]
 path = "../zino-core"
-version = "0.3.1"
+version = "0.4.0"
 
 [dependencies.zino-derive]
 path = "../zino-derive"
-version = "0.3.1"
\ No newline at end of file
+version = "0.3.2"
\ No newline at end of file
diff --git a/zino-model/src/collection.rs b/zino-model/src/collection.rs
index 1e11a63..c1fca93 100644
--- a/zino-model/src/collection.rs
+++ b/zino-model/src/collection.rs
@@ -1,5 +1,5 @@
 use serde::{Deserialize, Serialize};
-use zino_core::{DateTime, Map, Model, Schema, Uuid, Validation};
+use zino_core::{database::Model, datetime::DateTime, request::Validation, Map, Uuid};
 use zino_derive::Schema;
 
 /// The collection model.
diff --git a/zino-model/src/dataset.rs b/zino-model/src/dataset.rs
index 8715ff5..dda9838 100644
--- a/zino-model/src/dataset.rs
+++ b/zino-model/src/dataset.rs
@@ -1,5 +1,5 @@
 use serde::{Deserialize, Serialize};
-use zino_core::{DateTime, Map, Model, Schema, Uuid, Validation};
+use zino_core::{database::Model, datetime::DateTime, request::Validation, Map, Uuid};
 use zino_derive::Schema;
 
 /// The dataset model.
diff --git a/zino-model/src/group.rs b/zino-model/src/group.rs
index a301dcc..6fd4bfd 100644
--- a/zino-model/src/group.rs
+++ b/zino-model/src/group.rs
@@ -1,6 +1,6 @@
 use crate::User;
 use serde::{Deserialize, Serialize};
-use zino_core::{DateTime, Map, Model, Schema, Uuid, Validation};
+use zino_core::{database::Model, datetime::DateTime, request::Validation, Map, Uuid};
 use zino_derive::Schema;
 
 /// The group model.
diff --git a/zino-model/src/lib.rs b/zino-model/src/lib.rs
index fcf6696..d7e8cdd 100644
--- a/zino-model/src/lib.rs
+++ b/zino-model/src/lib.rs
@@ -23,7 +23,6 @@ mod task;
 mod log;
 mod record;
 
-// Reexports.
 pub use group::Group;
 pub use policy::Policy;
 pub use resource::Resource;
diff --git a/zino-model/src/log.rs b/zino-model/src/log.rs
index b9529bc..9584e9e 100644
--- a/zino-model/src/log.rs
+++ b/zino-model/src/log.rs
@@ -1,5 +1,5 @@
 use serde::{Deserialize, Serialize};
-use zino_core::{DateTime, Map, Model, Schema, Uuid, Validation};
+use zino_core::{database::Model, datetime::DateTime, request::Validation, Map, Uuid};
 use zino_derive::Schema;
 
 /// The log model.
diff --git a/zino-model/src/message.rs b/zino-model/src/message.rs
index 84cc08c..13d849e 100644
--- a/zino-model/src/message.rs
+++ b/zino-model/src/message.rs
@@ -1,5 +1,5 @@
 use serde::{Deserialize, Serialize};
-use zino_core::{DateTime, Map, Model, Schema, Uuid, Validation};
+use zino_core::{database::Model, datetime::DateTime, request::Validation, Map, Uuid};
 use zino_derive::Schema;
 
 /// The message model.
diff --git a/zino-model/src/order.rs b/zino-model/src/order.rs
index 5f480c8..87d7ef4 100644
--- a/zino-model/src/order.rs
+++ b/zino-model/src/order.rs
@@ -1,6 +1,6 @@
 use crate::Resource;
 use serde::{Deserialize, Serialize};
-use zino_core::{DateTime, Map, Model, Schema, Uuid, Validation};
+use zino_core::{database::Model, datetime::DateTime, request::Validation, Map, Uuid};
 use zino_derive::Schema;
 
 /// The order model.
diff --git a/zino-model/src/policy.rs b/zino-model/src/policy.rs
index 195921b..62dfde1 100644
--- a/zino-model/src/policy.rs
+++ b/zino-model/src/policy.rs
@@ -1,5 +1,5 @@
 use serde::{Deserialize, Serialize};
-use zino_core::{DateTime, Map, Model, Schema, Uuid, Validation};
+use zino_core::{database::Model, datetime::DateTime, request::Validation, Map, Uuid};
 use zino_derive::Schema;
 
 /// The policy model.
diff --git a/zino-model/src/record.rs b/zino-model/src/record.rs
index f1b3fa2..3d6683d 100644
--- a/zino-model/src/record.rs
+++ b/zino-model/src/record.rs
@@ -1,5 +1,5 @@
 use serde::{Deserialize, Serialize};
-use zino_core::{DateTime, Map, Model, Schema, Uuid, Validation};
+use zino_core::{database::Model, datetime::DateTime, request::Validation, Map, Uuid};
 use zino_derive::Schema;
 
 /// The record model.
diff --git a/zino-model/src/resource.rs b/zino-model/src/resource.rs
index eb794dc..b85fcc9 100644
--- a/zino-model/src/resource.rs
+++ b/zino-model/src/resource.rs
@@ -1,5 +1,5 @@
 use serde::{Deserialize, Serialize};
-use zino_core::{DateTime, Map, Model, Schema, Uuid, Validation};
+use zino_core::{database::Model, datetime::DateTime, request::Validation, Map, Uuid};
 use zino_derive::Schema;
 
 /// The resource model.
diff --git a/zino-model/src/source.rs b/zino-model/src/source.rs
index e06396b..7a53adc 100644
--- a/zino-model/src/source.rs
+++ b/zino-model/src/source.rs
@@ -1,5 +1,5 @@
 use serde::{Deserialize, Serialize};
-use zino_core::{DateTime, Map, Model, Schema, Uuid, Validation};
+use zino_core::{database::Model, datetime::DateTime, request::Validation, Map, Uuid};
 use zino_derive::Schema;
 
 /// The source model.
diff --git a/zino-model/src/tag.rs b/zino-model/src/tag.rs
index 7d66027..3a2465f 100644
--- a/zino-model/src/tag.rs
+++ b/zino-model/src/tag.rs
@@ -1,5 +1,5 @@
 use serde::{Deserialize, Serialize};
-use zino_core::{DateTime, Map, Model, Schema, Uuid, Validation};
+use zino_core::{database::Model, datetime::DateTime, request::Validation, Map, Uuid};
 use zino_derive::Schema;
 
 /// The tag model.
diff --git a/zino-model/src/task.rs b/zino-model/src/task.rs
index fabd5ca..8493d8a 100644
--- a/zino-model/src/task.rs
+++ b/zino-model/src/task.rs
@@ -1,5 +1,5 @@
 use serde::{Deserialize, Serialize};
-use zino_core::{DateTime, Map, Model, Schema, Uuid, Validation};
+use zino_core::{database::Model, datetime::DateTime, request::Validation, Map, Uuid};
 use zino_derive::Schema;
 
 /// The task model.
diff --git a/zino-model/src/user.rs b/zino-model/src/user.rs
index cef1206..bc4a699 100644
--- a/zino-model/src/user.rs
+++ b/zino-model/src/user.rs
@@ -1,5 +1,8 @@
 use serde::{Deserialize, Serialize};
-use zino_core::{AccessKeyId, DateTime, Map, Model, Schema, Uuid, Validation};
+use zino_core::{
+    authentication::AccessKeyId, database::Model, datetime::DateTime, request::Validation, Map,
+    Uuid,
+};
 use zino_derive::Schema;
 
 /// The user model.
diff --git a/zino/Cargo.toml b/zino/Cargo.toml
index 230a748..218e68c 100644
--- a/zino/Cargo.toml
+++ b/zino/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "zino"
 description = "Full featured web application framework for Rust."
-version = "0.3.1"
+version = "0.4.0"
 rust-version = "1.68"
 edition = "2021"
 license = "MIT"
@@ -13,13 +13,10 @@ documentation = "https://docs.rs/zino"
 readme = "README.md"
 
 [features]
-default = ["axum-server"]
-axum-server = ["dep:axum", "dep:tokio", "dep:tokio-stream", "dep:tower", "dep:tower-http"]
+axum = ["dep:axum", "dep:tokio", "dep:tokio-stream", "dep:tower", "dep:tower-http"]
 
 [dependencies]
 async-trait = { version = "0.1.60" }
-axum = { version = "0.6.1", features = ["ws"], optional = true }
-cfg-if = { version = "1.0.0" }
 futures = { version = "0.3.25" }
 http-types = { version = "2.12.0" }
 hyper = { version = "0.14.23" }
@@ -28,13 +25,16 @@ serde = { version = "1.0.152", features = ["derive"] }
 serde_json = { version = "1.0.91" }
 serde_qs = { version = "0.10.1" }
 serde_urlencoded = { version = "0.7.1" }
+toml = { version = "0.5.10" }
+tracing = { version = "0.1.37" }
+
+# optional dependencies
+axum = { version = "0.6.1", features = ["ws"], optional = true }
 tokio = { version = "1.24.1", features = ["rt-multi-thread", "sync", "parking_lot"], optional = true }
 tokio-stream = { version = "0.1.11", features = ["sync"], optional = true }
-toml = { version = "0.5.10" }
 tower = { version = "0.4.13", features = ["timeout"], optional = true }
 tower-http = { version = "0.3.5", features = ["full"], optional = true }
-tracing = { version = "0.1.37" }
 
 [dependencies.zino-core]
 path = "../zino-core"
-version = "0.3.1"
\ No newline at end of file
+version = "0.4.0"
\ No newline at end of file
diff --git a/zino/README.md b/zino/README.md
index ceb6c07..ad0a1df 100644
--- a/zino/README.md
+++ b/zino/README.md
@@ -16,7 +16,12 @@ productivity and performance.
 
 You can start with the example [`axum-app`].
 
+## Feature flags
+
+Currently, we only provide the `axum` feature to enable an integration with [`axum`].
+
 [`sqlx`]: https://crates.io/crates/sqlx
 [`tracing`]: https://crates.io/crates/tracing
 [`metrics`]: https://crates.io/crates/metrics
+[`axum`]: https://crates.io/crates/axum
 [`axum-app`]: https://github.com/photino/zino/tree/main/examples/axum-app
\ No newline at end of file
diff --git a/zino/src/channel/axum_channel.rs b/zino/src/channel/axum_channel.rs
index 3871d31..5cde11a 100644
--- a/zino/src/channel/axum_channel.rs
+++ b/zino/src/channel/axum_channel.rs
@@ -3,7 +3,11 @@ use parking_lot::RwLock;
 use std::{collections::HashMap, sync::LazyLock};
 use tokio::sync::mpsc::{self, error::TrySendError, Receiver, Sender};
 use tokio_stream::wrappers::ReceiverStream;
-use zino_core::{Application, CloudEvent, Subscription, Uuid};
+use zino_core::{
+    application::Application,
+    channel::{CloudEvent, Subscription},
+    Uuid,
+};
 
 /// A emitter is a sender of cloud events.
 type Emitter = Sender<CloudEvent>;
diff --git a/zino/src/channel/mod.rs b/zino/src/channel/mod.rs
index 5f0e74b..68eaa13 100644
--- a/zino/src/channel/mod.rs
+++ b/zino/src/channel/mod.rs
@@ -1,2 +1,2 @@
-#[cfg(feature = "axum-server")]
+#[cfg(feature = "axum")]
 pub(crate) mod axum_channel;
diff --git a/zino/src/cluster/axum_cluster.rs b/zino/src/cluster/axum_cluster.rs
index b090fa8..70e2835 100644
--- a/zino/src/cluster/axum_cluster.rs
+++ b/zino/src/cluster/axum_cluster.rs
@@ -20,7 +20,14 @@ use tower_http::{
     compression::CompressionLayer,
     services::{ServeDir, ServeFile},
 };
-use zino_core::{Application, AsyncCronJob, DateTime, Job, JobScheduler, Map, Response, State};
+use zino_core::{
+    application::Application,
+    datetime::DateTime,
+    response::Response,
+    schedule::{AsyncCronJob, Job, JobScheduler},
+    state::State,
+    Map,
+};
 
 /// An HTTP server cluster for `axum`.
 pub struct AxumCluster {
diff --git a/zino/src/cluster/mod.rs b/zino/src/cluster/mod.rs
index f98e2bf..31039c2 100644
--- a/zino/src/cluster/mod.rs
+++ b/zino/src/cluster/mod.rs
@@ -1,2 +1,2 @@
-#[cfg(feature = "axum-server")]
-pub mod axum_cluster;
+#[cfg(feature = "axum")]
+pub(crate) mod axum_cluster;
diff --git a/zino/src/endpoint/axum_sse.rs b/zino/src/endpoint/axum_sse.rs
index bb20e29..fc0ee66 100644
--- a/zino/src/endpoint/axum_sse.rs
+++ b/zino/src/endpoint/axum_sse.rs
@@ -5,7 +5,7 @@ use axum::{
 use futures::stream::Stream;
 use std::convert::Infallible;
 use tokio_stream::StreamExt;
-use zino_core::Subscription;
+use zino_core::channel::Subscription;
 
 /// SSE endpoint handler.
 pub(crate) async fn sse_handler(
diff --git a/zino/src/endpoint/axum_websocket.rs b/zino/src/endpoint/axum_websocket.rs
index ad2e962..56f39d8 100644
--- a/zino/src/endpoint/axum_websocket.rs
+++ b/zino/src/endpoint/axum_websocket.rs
@@ -5,7 +5,7 @@ use axum::{
     },
     response::IntoResponse,
 };
-use zino_core::{CloudEvent, Subscription};
+use zino_core::channel::{CloudEvent, Subscription};
 
 /// WebSocket endpoint handler.
 pub(crate) async fn websocket_handler(
diff --git a/zino/src/endpoint/mod.rs b/zino/src/endpoint/mod.rs
index aacb656..9c9061e 100644
--- a/zino/src/endpoint/mod.rs
+++ b/zino/src/endpoint/mod.rs
@@ -1,6 +1,5 @@
-cfg_if::cfg_if! {
-    if #[cfg(feature = "axum-server")] {
-        pub(crate) mod axum_sse;
-        pub(crate) mod axum_websocket;
-    }
-}
+#[cfg(feature = "axum")]
+pub(crate) mod axum_sse;
+
+#[cfg(feature = "axum")]
+pub(crate) mod axum_websocket;
diff --git a/zino/src/lib.rs b/zino/src/lib.rs
index bd8a1fa..ad9bc99 100644
--- a/zino/src/lib.rs
+++ b/zino/src/lib.rs
@@ -14,13 +14,19 @@
 //!
 //! You can start with the example [`axum-app`].
 //!
+//! ## Feature flags
+//!
+//! Currently, we only provide the `axum` feature to enable an integration with [`axum`].
+//!
 //! [`zino`]: https://github.com/photino/zino
 //! [`sqlx`]: https://crates.io/crates/sqlx
 //! [`tracing`]: https://crates.io/crates/tracing
 //! [`metrics`]: https://crates.io/crates/metrics
+//! [`axum`]: https://crates.io/crates/axum
 //! [`axum-app`]: https://github.com/photino/zino/tree/main/examples/axum-app
 
 #![feature(async_fn_in_trait)]
+#![feature(doc_auto_cfg)]
 #![feature(once_cell)]
 #![feature(result_option_inspect)]
 #![feature(string_leak)]
@@ -32,17 +38,32 @@ mod endpoint;
 mod middleware;
 mod request;
 
-cfg_if::cfg_if! {
-    if #[cfg(feature = "axum-server")] {
-        // Reexports.
-        pub use cluster::axum_cluster::AxumCluster;
-        pub use request::axum_request::AxumExtractor;
+#[cfg(feature = "axum")]
+pub use cluster::axum_cluster::AxumCluster;
 
-        /// A specialized request extractor for `axum`.
-        pub type Request = AxumExtractor<axum::http::Request<axum::body::Body>>;
+#[cfg(feature = "axum")]
+pub use request::axum_request::AxumExtractor;
 
-        /// A specialized `Result` type for `axum`.
-        pub type Result<T = axum::http::Response<axum::body::Full<axum::body::Bytes>>> =
-            std::result::Result<T, T>;
-    }
-}
+#[cfg(feature = "axum")]
+/// A specialized request extractor for `axum`.
+pub type Request = AxumExtractor<axum::http::Request<axum::body::Body>>;
+
+#[cfg(feature = "axum")]
+/// A specialized `Result` type for `axum`.
+pub type Result<T = axum::http::Response<axum::body::Full<axum::body::Bytes>>> =
+    std::result::Result<T, T>;
+
+#[doc(no_inline)]
+pub use zino_core::{
+    application::Application,
+    authentication::{AccessKeyId, Authentication, SecretAccessKey, SecurityToken},
+    cache::GlobalCache,
+    channel::{CloudEvent, Subscription},
+    database::{Column, ConnectionPool, Model, Mutation, Query, Schema},
+    datetime::DateTime,
+    request::{Context, RequestContext, Validation},
+    response::{Rejection, Response, ResponseCode},
+    schedule::{AsyncCronJob, CronJob, Job, JobScheduler},
+    state::State,
+    BoxError, BoxFuture, Map, Uuid,
+};
diff --git a/zino/src/middleware/axum_context.rs b/zino/src/middleware/axum_context.rs
index 9b13e11..1d536ac 100644
--- a/zino/src/middleware/axum_context.rs
+++ b/zino/src/middleware/axum_context.rs
@@ -3,7 +3,7 @@ use axum::{
     http::{Request, Response, StatusCode},
     middleware::Next,
 };
-use zino_core::RequestContext;
+use zino_core::request::RequestContext;
 
 pub(crate) async fn request_context(
     req: Request<Body>,
diff --git a/zino/src/middleware/mod.rs b/zino/src/middleware/mod.rs
index 0e272b4..2f0936c 100644
--- a/zino/src/middleware/mod.rs
+++ b/zino/src/middleware/mod.rs
@@ -1,7 +1,8 @@
-cfg_if::cfg_if! {
-    if #[cfg(feature = "axum-server")] {
-        pub(crate) mod axum_context;
-        pub(crate) mod tower_cors;
-        pub(crate) mod tower_tracing;
-    }
-}
+#[cfg(feature = "axum")]
+pub(crate) mod axum_context;
+
+#[cfg(feature = "axum")]
+pub(crate) mod tower_cors;
+
+#[cfg(feature = "axum")]
+pub(crate) mod tower_tracing;
diff --git a/zino/src/middleware/tower_cors.rs b/zino/src/middleware/tower_cors.rs
index 0b6a390..6103c40 100644
--- a/zino/src/middleware/tower_cors.rs
+++ b/zino/src/middleware/tower_cors.rs
@@ -1,6 +1,6 @@
 use std::{sync::LazyLock, time::Duration};
 use tower_http::cors::{AllowHeaders, AllowMethods, AllowOrigin, CorsLayer, ExposeHeaders};
-use zino_core::Application;
+use zino_core::application::Application;
 
 // CORS middleware.
 pub(crate) static CORS_MIDDLEWARE: LazyLock<CorsLayer> = LazyLock::new(|| {
diff --git a/zino/src/request/axum_request.rs b/zino/src/request/axum_request.rs
index 391a819..c2d55fd 100644
--- a/zino/src/request/axum_request.rs
+++ b/zino/src/request/axum_request.rs
@@ -11,7 +11,13 @@ use std::{
     ops::{Deref, DerefMut},
 };
 use toml::value::Table;
-use zino_core::{CloudEvent, Context, Map, Rejection, RequestContext, State, Validation};
+use zino_core::{
+    channel::CloudEvent,
+    request::{Context, RequestContext, Validation},
+    response::Rejection,
+    state::State,
+    Map,
+};
 
 /// An HTTP request extractor for `axum`.
 pub struct AxumExtractor<T>(pub(crate) T);
diff --git a/zino/src/request/mod.rs b/zino/src/request/mod.rs
index 83c26f5..5d0b805 100644
--- a/zino/src/request/mod.rs
+++ b/zino/src/request/mod.rs
@@ -1,2 +1,2 @@
-#[cfg(feature = "axum-server")]
-pub mod axum_request;
+#[cfg(feature = "axum")]
+pub(crate) mod axum_request;