diff --git a/db/Cargo.toml b/db/Cargo.toml
index 60d1e735..634d9d1a 100644
--- a/db/Cargo.toml
+++ b/db/Cargo.toml
@@ -5,6 +5,7 @@ workspace = ".."
 
 [dependencies]
 error-chain = { git = "https://github.com/rnewman/error-chain", branch = "rnewman/sync" }
+indexmap = "0.4"
 itertools = "0.7"
 lazy_static = "0.2"
 num = "0.1"
diff --git a/db/src/lib.rs b/db/src/lib.rs
index 19e9619b..d91c7568 100644
--- a/db/src/lib.rs
+++ b/db/src/lib.rs
@@ -13,6 +13,7 @@
 
 #[macro_use]
 extern crate error_chain;
+extern crate indexmap;
 extern crate itertools;
 
 #[macro_use]
@@ -45,6 +46,7 @@ pub mod errors;
 pub mod internal_types;    // pub because we need them for building entities programmatically.
 mod metadata;
 mod schema;
+pub mod tx_observer;
 mod watcher;
 mod tx;
 pub mod types;
diff --git a/db/src/tx_observer.rs b/db/src/tx_observer.rs
new file mode 100644
index 00000000..240e9ae0
--- /dev/null
+++ b/db/src/tx_observer.rs
@@ -0,0 +1,171 @@
+// Copyright 2018 Mozilla
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
+// this file except in compliance with the License. You may obtain a copy of the
+// License at http://www.apache.org/licenses/LICENSE-2.0
+// Unless required by applicable law or agreed to in writing, software distributed
+// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+// CONDITIONS OF ANY KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations under the License.
+
+use std::sync::{
+    Arc,
+};
+use std::thread;
+
+use indexmap::{
+    IndexMap,
+};
+
+use types::{
+    AttributeSet,
+    TxReport,
+};
+
+pub struct TxObserver {
+    notify_fn: Arc<Option<Box<Fn(String, Vec<TxReport>) + Send + Sync>>>,
+    attributes: AttributeSet,
+}
+
+impl TxObserver {
+    pub fn new<F>(attributes: AttributeSet, notify_fn: F) -> TxObserver where F: Fn(String, Vec<TxReport>) + 'static + Send + Sync {
+        TxObserver {
+            notify_fn: Arc::new(Some(Box::new(notify_fn))),
+            attributes,
+        }
+    }
+
+    pub fn applicable_reports(&self, reports: &Vec<TxReport>) -> Vec<TxReport> {
+        reports.into_iter().filter_map( |report| {
+            if self.attributes.intersection(&report.changeset).next().is_some(){
+                Some(report.clone())
+            } else {
+                None
+            }
+        }).collect()
+    }
+
+    fn notify(&self, key: String, reports: Vec<TxReport>) {
+        if let Some(ref notify_fn) = *self.notify_fn {
+            (notify_fn)(key, reports);
+        } else {
+            eprintln!("no notify function specified for TxObserver");
+        }
+    }
+}
+
+pub trait CommandClone {
+    fn clone_box(&self) -> Box<Command + Send>;
+}
+
+impl<T> CommandClone for T where T: 'static + Command + Clone + Send {
+    fn clone_box(&self) -> Box<Command + Send> {
+        Box::new(self.clone())
+    }
+}
+
+pub trait Command: CommandClone {
+    fn execute(&self);
+}
+
+impl Clone for Box<Command + Send> {
+    fn clone(&self) -> Box<Command + Send> {
+        self.clone_box()
+    }
+}
+
+#[derive(Clone)]
+pub struct NotifyTxObserver {
+    key: String,
+    reports: Vec<TxReport>,
+    observer: Arc<TxObserver>,
+}
+
+impl NotifyTxObserver {
+    pub fn new(key: String, reports: Vec<TxReport>, observer: Arc<TxObserver>) -> Self {
+        NotifyTxObserver {
+            key,
+            reports,
+            observer,
+        }
+    }
+}
+
+impl Command for NotifyTxObserver {
+    fn execute(&self) {
+        self.observer.notify(self.key.clone(), self.reports.clone());
+    }
+}
+
+#[derive(Clone)]
+pub struct AsyncBatchExecutor {
+    commands: Vec<Box<Command + Send>>,
+}
+
+impl Command for AsyncBatchExecutor {
+    fn execute(&self) {
+        let command_queue = self.commands.clone();
+        thread::spawn (move ||{
+            for command in command_queue.iter() {
+                command.execute();
+            }
+        });
+    }
+}
+
+#[derive(Clone)]
+pub struct TxObservationService {
+    observers: IndexMap<String, Arc<TxObserver>>,
+    pub command_queue: Vec<Box<Command + Send>>,
+}
+
+impl TxObservationService {
+    pub fn new() -> Self {
+        TxObservationService {
+            observers: IndexMap::new(),
+            command_queue: Vec::new(),
+        }
+    }
+    // For testing purposes
+    pub fn is_registered(&self, key: &String) -> bool {
+        self.observers.contains_key(key)
+    }
+
+    pub fn register(&mut self, key: String, observer: Arc<TxObserver>) {
+        self.observers.insert(key.clone(), observer);
+    }
+
+    pub fn deregister(&mut self, key: &String) {
+        self.observers.remove(key);
+    }
+
+    pub fn has_observers(&self) -> bool {
+        !self.observers.is_empty()
+    }
+
+    fn command_from_reports(&self, key: &String, reports: &Vec<TxReport>, observer: &Arc<TxObserver>) -> Option<Box<Command + Send>> {
+        let applicable_reports = observer.applicable_reports(reports);
+        if !applicable_reports.is_empty() {
+            Some(Box::new(NotifyTxObserver::new(key.clone(), applicable_reports, Arc::clone(observer))))
+        } else {
+            None
+        }
+    }
+
+    pub fn transaction_did_commit(&mut self, reports: Vec<TxReport>) {
+        // notify all observers about their relevant transactions
+        let commands: Vec<Box<Command + Send>> = self.observers
+                                                .iter()
+                                                .filter_map(|(key, observer)| { self.command_from_reports(&key, &reports, &observer) })
+                                                .collect();
+        self.command_queue.push(Box::new(AsyncBatchExecutor{ commands }));
+    }
+
+    pub fn run(&mut self) {
+        for command in self.command_queue.iter() {
+            command.execute();
+        }
+
+        self.command_queue.clear();
+    }
+}
diff --git a/db/src/types.rs b/db/src/types.rs
index 4fd40bd5..5e19da73 100644
--- a/db/src/types.rs
+++ b/db/src/types.rs
@@ -11,19 +11,22 @@
 #![allow(dead_code)]
 
 use std::collections::HashMap;
-use std::collections::BTreeMap;
+use std::collections::{
+    BTreeMap,
+    BTreeSet,
+};
 
 extern crate mentat_core;
 
 pub use self::mentat_core::{
-    DateTime,
-    Entid,
-    ValueType,
-    TypedValue,
     Attribute,
     AttributeBitFlags,
+    DateTime,
+    Entid,
     Schema,
+    TypedValue,
     Utc,
+    ValueType,
 };
 
 /// Represents one partition of the entid space.
@@ -82,6 +85,9 @@ pub type AVPair = (Entid, TypedValue);
 /// Used to resolve lookup-refs and upserts.
 pub type AVMap<'a> = HashMap<&'a AVPair, Entid>;
 
+// represents a set of entids that are correspond to attributes
+pub type AttributeSet = BTreeSet<Entid>;
+
 /// A transaction report summarizes an applied transaction.
 #[derive(Clone, Debug, Eq, Hash, Ord, PartialOrd, PartialEq)]
 pub struct TxReport {
@@ -97,4 +103,7 @@ pub struct TxReport {
     /// existing entid, or is allocated a new entid.  (It is possible for multiple distinct string
     /// literal tempids to all unify to a single freshly allocated entid.)
     pub tempids: BTreeMap<String, Entid>,
+
+    // A set of entids for attributes that were affected inside this transaction
+    pub changeset: AttributeSet,
 }