diff --git a/Cargo.toml b/Cargo.toml
index 0a751e9..b19c11b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,3 +16,4 @@ url = { version = "2.2", features = ["serde"] }
 bitflags = "1.2"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
+async-trait = "0.1"
diff --git a/src/lib.rs b/src/lib.rs
index 1724ca4..1df735f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -8,6 +8,8 @@
 //! A `Provider` abstracts these two sources by merging them together into one virtual source. \
 //! It also handles synchronisation between the local cache and the server.
 
+pub mod traits;
+
 pub mod calendar;
 pub use calendar::Calendar;
 mod task;
diff --git a/src/traits.rs b/src/traits.rs
index 6d530ef..2fc9e38 100644
--- a/src/traits.rs
+++ b/src/traits.rs
@@ -1,49 +1,16 @@
-//! This module provides CalDAV data sources and utilities
-
-/*
 use std::error::Error;
 
+use async_trait::async_trait;
 
+use crate::Calendar;
 
-/// A Caldav data source
-pub struct DataSource {
-    client: Option<Client>,
+#[async_trait]
+pub trait CalDavSource {
+    /// Returns the current calendars that this source contains
+    /// This function may trigger an update (that can be a long process, or that can even fail, e.g. in case of a remote server)
+    async fn get_calendars(&self) -> Result<&Vec<Calendar>, Box<dyn Error>>;
 
-    calendars: Vec<Calendar>
+    /// Returns the current calendars that this source contains
+    /// This function may trigger an update (that can be a long process, or that can even fail, e.g. in case of a remote server)
+    async fn get_calendars_mut(&mut self) -> Result<Vec<&mut Calendar>, Box<dyn Error>>;
 }
-
-impl DataSource {
-    /// Create a new data source
-    pub fn new() -> Self {
-        Self{
-            client: None,
-            calendars: Vec::new(),
-        }
-    }
-
-    /// Tell this data source what the source server is
-    pub fn set_server(&mut self, url: String, username: String, password: String) -> Result<(), Box<dyn Error>> {
-        self.client = Some(Client::new(url, username, password)?);
-        Ok(())
-    }
-
-    /// Update the local database with info from the Client
-    pub fn fetch_from_server(&mut self) {
-        // TODO: how to handle conflicts?
-    }
-
-    pub fn update_changes_to_server(&self) {
-
-    }
-
-    // TODO: the API should force calling fetch_from_server before
-    pub fn calendars(&self) -> Vec<&Calendar> {
-        // TODO: what happens when a user has a reference, which is modified/updated from the server? Conflict mut/not mut?
-        // TODO: how can the user modify Tasks from a non-mut reference?
-        self.calendars
-            .iter()
-            .collect()
-    }
-}
-
-*/