diff --git a/lib/src/sparql/dataset.rs b/lib/src/sparql/dataset.rs
index f54cc2f9..2e782308 100644
--- a/lib/src/sparql/dataset.rs
+++ b/lib/src/sparql/dataset.rs
@@ -1,10 +1,11 @@
 use crate::sparql::algebra::QueryDataset;
 use crate::sparql::EvaluationError;
 use crate::storage::numeric_encoder::{
-    EncodedQuad, EncodedTerm, ReadEncoder, StrContainer, StrEncodingAware, StrHash, StrLookup,
+    EncodedQuad, EncodedTerm, ReadEncoder, StrContainer, StrHash, StrLookup,
 };
 use crate::storage::Storage;
 use std::cell::RefCell;
+use std::collections::hash_map::Entry;
 use std::collections::HashMap;
 use std::iter::empty;
 
@@ -154,40 +155,34 @@ impl DatasetView {
     }
 }
 
-impl StrEncodingAware for DatasetView {
+impl StrLookup for DatasetView {
     type Error = EvaluationError;
-}
 
-impl StrLookup for DatasetView {
-    fn get_str(&self, id: StrHash) -> Result<Option<String>, EvaluationError> {
-        Ok(if let Some(value) = self.extra.borrow().get(&id) {
+    fn get_str(&self, key: StrHash) -> Result<Option<String>, EvaluationError> {
+        Ok(if let Some(value) = self.extra.borrow().get(&key) {
             Some(value.clone())
         } else {
-            self.storage.get_str(id)?
+            self.storage.get_str(key)?
         })
     }
 
-    fn get_str_id(&self, value: &str) -> Result<Option<StrHash>, EvaluationError> {
-        let id = StrHash::new(value);
-        Ok(if self.extra.borrow().contains_key(&id) {
-            Some(id)
-        } else {
-            self.storage.get_str_id(value)?
-        })
+    fn contains_str(&self, key: StrHash) -> Result<bool, EvaluationError> {
+        Ok(self.extra.borrow().contains_key(&key) || self.storage.contains_str(key)?)
     }
 }
 
 impl StrContainer for DatasetView {
-    fn insert_str(&self, value: &str) -> Result<StrHash, EvaluationError> {
-        if let Some(hash) = self.storage.get_str_id(value)? {
-            Ok(hash)
+    fn insert_str(&self, key: StrHash, value: &str) -> Result<bool, EvaluationError> {
+        if self.storage.contains_str(key)? {
+            Ok(false)
         } else {
-            let hash = StrHash::new(value);
-            self.extra
-                .borrow_mut()
-                .entry(hash)
-                .or_insert_with(|| value.to_owned());
-            Ok(hash)
+            match self.extra.borrow_mut().entry(key) {
+                Entry::Occupied(_) => Ok(false),
+                Entry::Vacant(entry) => {
+                    entry.insert(value.to_owned());
+                    Ok(true)
+                }
+            }
         }
     }
 }
diff --git a/lib/src/storage/binary_encoder.rs b/lib/src/storage/binary_encoder.rs
index 1ddb729c..80c453ba 100644
--- a/lib/src/storage/binary_encoder.rs
+++ b/lib/src/storage/binary_encoder.rs
@@ -628,43 +628,37 @@ pub fn write_term(sink: &mut Vec<u8>, term: EncodedTerm) {
 mod tests {
     use super::*;
     use crate::storage::numeric_encoder::*;
+    use std::cell::RefCell;
+    use std::collections::hash_map::Entry;
     use std::collections::HashMap;
     use std::convert::Infallible;
-    use std::sync::RwLock;
 
     #[derive(Default)]
     struct MemoryStrStore {
-        id2str: RwLock<HashMap<StrHash, String>>,
+        id2str: RefCell<HashMap<StrHash, String>>,
     }
 
-    impl StrEncodingAware for MemoryStrStore {
+    impl StrLookup for MemoryStrStore {
         type Error = Infallible;
-    }
 
-    impl StrLookup for MemoryStrStore {
-        fn get_str(&self, id: StrHash) -> Result<Option<String>, Infallible> {
-            Ok(self.id2str.read().unwrap().get(&id).cloned())
+        fn get_str(&self, key: StrHash) -> Result<Option<String>, Infallible> {
+            Ok(self.id2str.borrow().get(&key).cloned())
         }
 
-        fn get_str_id(&self, value: &str) -> Result<Option<StrHash>, Infallible> {
-            let id = StrHash::new(value);
-            Ok(if self.id2str.read().unwrap().contains_key(&id) {
-                Some(id)
-            } else {
-                None
-            })
+        fn contains_str(&self, key: StrHash) -> Result<bool, Infallible> {
+            Ok(self.id2str.borrow().contains_key(&key))
         }
     }
 
     impl StrContainer for MemoryStrStore {
-        fn insert_str(&self, value: &str) -> Result<StrHash, Infallible> {
-            let key = StrHash::new(value);
-            self.id2str
-                .write()
-                .unwrap()
-                .entry(key)
-                .or_insert_with(|| value.to_owned());
-            Ok(key)
+        fn insert_str(&self, key: StrHash, value: &str) -> Result<bool, Infallible> {
+            match self.id2str.borrow_mut().entry(key) {
+                Entry::Occupied(_) => Ok(false),
+                Entry::Vacant(entry) => {
+                    entry.insert(value.to_owned());
+                    Ok(true)
+                }
+            }
         }
     }
 
diff --git a/lib/src/storage/mod.rs b/lib/src/storage/mod.rs
index 21e6f938..2de3c5e4 100644
--- a/lib/src/storage/mod.rs
+++ b/lib/src/storage/mod.rs
@@ -18,9 +18,7 @@ use crate::storage::binary_encoder::{
     LATEST_STORAGE_VERSION, WRITTEN_TERM_MAX_SIZE,
 };
 use crate::storage::io::StoreOrParseError;
-use crate::storage::numeric_encoder::{
-    EncodedQuad, EncodedTerm, StrContainer, StrEncodingAware, StrHash, StrLookup,
-};
+use crate::storage::numeric_encoder::{EncodedQuad, EncodedTerm, StrContainer, StrHash, StrLookup};
 
 mod binary_encoder;
 pub(crate) mod io;
@@ -991,57 +989,39 @@ impl<T> From<ConflictableTransactionError<T>> for Sled2ConflictableTransactionEr
     }
 }
 
-impl StrEncodingAware for Storage {
+impl StrLookup for Storage {
     type Error = std::io::Error;
-}
 
-impl StrLookup for Storage {
-    fn get_str(&self, id: StrHash) -> Result<Option<String>, std::io::Error> {
-        self.get_str(id)
+    fn get_str(&self, key: StrHash) -> Result<Option<String>, std::io::Error> {
+        self.get_str(key)
     }
 
-    fn get_str_id(&self, value: &str) -> Result<Option<StrHash>, std::io::Error> {
-        let key = StrHash::new(value);
-        Ok(if self.contains_str(key)? {
-            Some(key)
-        } else {
-            None
-        })
+    fn contains_str(&self, key: StrHash) -> Result<bool, std::io::Error> {
+        self.contains_str(key)
     }
 }
 
 impl StrContainer for Storage {
-    fn insert_str(&self, value: &str) -> Result<StrHash, std::io::Error> {
-        let key = StrHash::new(value);
-        self.insert_str(key, value)?;
-        Ok(key)
+    fn insert_str(&self, key: StrHash, value: &str) -> Result<bool, std::io::Error> {
+        self.insert_str(key, value)
     }
 }
 
-impl<'a> StrEncodingAware for StorageTransaction<'a> {
+impl<'a> StrLookup for StorageTransaction<'a> {
     type Error = UnabortableTransactionError;
-}
 
-impl<'a> StrLookup for StorageTransaction<'a> {
-    fn get_str(&self, id: StrHash) -> Result<Option<String>, UnabortableTransactionError> {
-        self.get_str(id)
+    fn get_str(&self, key: StrHash) -> Result<Option<String>, UnabortableTransactionError> {
+        self.get_str(key)
     }
 
-    fn get_str_id(&self, value: &str) -> Result<Option<StrHash>, UnabortableTransactionError> {
-        let key = StrHash::new(value);
-        Ok(if self.contains_str(key)? {
-            Some(key)
-        } else {
-            None
-        })
+    fn contains_str(&self, key: StrHash) -> Result<bool, UnabortableTransactionError> {
+        self.contains_str(key)
     }
 }
 
 impl<'a> StrContainer for StorageTransaction<'a> {
-    fn insert_str(&self, value: &str) -> Result<StrHash, UnabortableTransactionError> {
-        let key = StrHash::new(value);
-        self.insert_str(key, value)?;
-        Ok(key)
+    fn insert_str(&self, key: StrHash, value: &str) -> Result<bool, UnabortableTransactionError> {
+        self.insert_str(key, value)
     }
 }
 
diff --git a/lib/src/storage/numeric_encoder.rs b/lib/src/storage/numeric_encoder.rs
index 5c718cce..b6113a0f 100644
--- a/lib/src/storage/numeric_encoder.rs
+++ b/lib/src/storage/numeric_encoder.rs
@@ -486,27 +486,20 @@ impl EncodedQuad {
     }
 }
 
-pub(crate) trait StrEncodingAware {
-    //TODO: rename
+pub(crate) trait StrLookup {
     type Error: Error + Into<EvaluationError> + 'static;
-}
-
-impl<'a, T: StrEncodingAware> StrEncodingAware for &'a T {
-    type Error = T::Error;
-}
 
-pub(crate) trait StrLookup: StrEncodingAware {
-    fn get_str(&self, id: StrHash) -> Result<Option<String>, Self::Error>;
+    fn get_str(&self, key: StrHash) -> Result<Option<String>, Self::Error>;
 
-    fn get_str_id(&self, value: &str) -> Result<Option<StrHash>, Self::Error>;
+    fn contains_str(&self, key: StrHash) -> Result<bool, Self::Error>;
 }
 
-pub(crate) trait StrContainer: StrEncodingAware {
-    fn insert_str(&self, value: &str) -> Result<StrHash, Self::Error>;
+pub(crate) trait StrContainer: StrLookup {
+    fn insert_str(&self, key: StrHash, value: &str) -> Result<bool, Self::Error>;
 }
 
 /// Tries to encode a term based on the existing strings (does not insert anything)
-pub(crate) trait ReadEncoder: StrEncodingAware {
+pub(crate) trait ReadEncoder: StrLookup {
     fn get_encoded_named_node(
         &self,
         named_node: NamedNodeRef<'_>,
@@ -738,12 +731,17 @@ pub(crate) trait ReadEncoder: StrEncodingAware {
 
 impl<S: StrLookup> ReadEncoder for S {
     fn get_encoded_str(&self, value: &str) -> Result<Option<StrHash>, Self::Error> {
-        self.get_str_id(value)
+        let key = StrHash::new(value);
+        Ok(if self.contains_str(key)? {
+            Some(key)
+        } else {
+            None
+        })
     }
 }
 
 /// Encodes a term and insert strings if needed
-pub(crate) trait WriteEncoder: StrEncodingAware {
+pub(crate) trait WriteEncoder: StrContainer {
     fn encode_named_node(&self, named_node: NamedNodeRef<'_>) -> Result<EncodedTerm, Self::Error> {
         self.encode_rio_named_node(named_node.into())
     }
@@ -999,7 +997,9 @@ pub(crate) trait WriteEncoder: StrEncodingAware {
 
 impl<S: StrContainer> WriteEncoder for S {
     fn encode_str(&self, value: &str) -> Result<StrHash, Self::Error> {
-        self.insert_str(value)
+        let key = StrHash::new(value);
+        self.insert_str(key, value)?;
+        Ok(key)
     }
 }
 
diff --git a/lib/src/store.rs b/lib/src/store.rs
index fc776799..d2c5da45 100644
--- a/lib/src/store.rs
+++ b/lib/src/store.rs
@@ -42,10 +42,7 @@ use crate::sparql::{
     UpdateOptions,
 };
 use crate::storage::io::{dump_dataset, dump_graph, load_dataset, load_graph};
-use crate::storage::numeric_encoder::{
-    Decoder, EncodedTerm, ReadEncoder, StrContainer, StrEncodingAware, StrHash, StrLookup,
-    WriteEncoder,
-};
+use crate::storage::numeric_encoder::{Decoder, EncodedTerm, ReadEncoder, WriteEncoder};
 pub use crate::storage::ConflictableTransactionError;
 pub use crate::storage::TransactionError;
 pub use crate::storage::UnabortableTransactionError;
@@ -247,7 +244,7 @@ impl Store {
 
     /// Checks if this store contains a given quad
     pub fn contains<'a>(&self, quad: impl Into<QuadRef<'a>>) -> Result<bool, io::Error> {
-        if let Some(quad) = self.get_encoded_quad(quad.into())? {
+        if let Some(quad) = self.storage.get_encoded_quad(quad.into())? {
             self.storage.contains(&quad)
         } else {
             Ok(false)
@@ -431,7 +428,7 @@ impl Store {
     /// It might leave the store in a bad state if a crash happens during the insertion.
     /// Use a (memory greedy) [transaction](Store::transaction()) if you do not want that.
     pub fn insert<'a>(&self, quad: impl Into<QuadRef<'a>>) -> Result<bool, io::Error> {
-        let quad = self.encode_quad(quad.into())?;
+        let quad = self.storage.encode_quad(quad.into())?;
         self.storage.insert(&quad)
     }
 
@@ -443,7 +440,7 @@ impl Store {
     /// It might leave the store in a bad state if a crash happens during the removal.
     /// Use a (memory greedy) [transaction](Store::transaction()) if you do not want that.
     pub fn remove<'a>(&self, quad: impl Into<QuadRef<'a>>) -> Result<bool, io::Error> {
-        if let Some(quad) = self.get_encoded_quad(quad.into())? {
+        if let Some(quad) = self.storage.get_encoded_quad(quad.into())? {
             self.storage.remove(&quad)
         } else {
             Ok(false)
@@ -540,7 +537,10 @@ impl Store {
         &self,
         graph_name: impl Into<NamedOrBlankNodeRef<'a>>,
     ) -> Result<bool, io::Error> {
-        if let Some(graph_name) = self.get_encoded_named_or_blank_node(graph_name.into())? {
+        if let Some(graph_name) = self
+            .storage
+            .get_encoded_named_or_blank_node(graph_name.into())?
+        {
             self.storage.contains_named_graph(graph_name)
         } else {
             Ok(false)
@@ -566,7 +566,7 @@ impl Store {
         &self,
         graph_name: impl Into<NamedOrBlankNodeRef<'a>>,
     ) -> Result<bool, io::Error> {
-        let graph_name = self.encode_named_or_blank_node(graph_name.into())?;
+        let graph_name = self.storage.encode_named_or_blank_node(graph_name.into())?;
         self.storage.insert_named_graph(graph_name)
     }
 
@@ -592,7 +592,7 @@ impl Store {
         &self,
         graph_name: impl Into<GraphNameRef<'a>>,
     ) -> Result<(), io::Error> {
-        if let Some(graph_name) = self.get_encoded_graph_name(graph_name.into())? {
+        if let Some(graph_name) = self.storage.get_encoded_graph_name(graph_name.into())? {
             self.storage.clear_graph(graph_name)
         } else {
             Ok(())
@@ -623,7 +623,10 @@ impl Store {
         &self,
         graph_name: impl Into<NamedOrBlankNodeRef<'a>>,
     ) -> Result<bool, io::Error> {
-        if let Some(graph_name) = self.get_encoded_named_or_blank_node(graph_name.into())? {
+        if let Some(graph_name) = self
+            .storage
+            .get_encoded_named_or_blank_node(graph_name.into())?
+        {
             self.storage.remove_named_graph(graph_name)
         } else {
             Ok(false)
@@ -661,28 +664,6 @@ impl fmt::Display for Store {
     }
 }
 
-impl StrEncodingAware for Store {
-    type Error = io::Error;
-}
-
-impl StrLookup for Store {
-    fn get_str(&self, id: StrHash) -> Result<Option<String>, io::Error> {
-        self.storage.get_str(id)
-    }
-
-    fn get_str_id(&self, value: &str) -> Result<Option<StrHash>, io::Error> {
-        self.storage.get_str_id(value)
-    }
-}
-
-impl<'a> StrContainer for &'a Store {
-    fn insert_str(&self, value: &str) -> Result<StrHash, io::Error> {
-        let key = StrHash::new(value);
-        self.storage.insert_str(key, value)?;
-        Ok(key)
-    }
-}
-
 /// Allows inserting and deleting quads during an ACID transaction with the [`Store`].
 pub struct Transaction<'a> {
     storage: StorageTransaction<'a>,
@@ -792,7 +773,7 @@ impl Transaction<'_> {
         &self,
         quad: impl Into<QuadRef<'a>>,
     ) -> Result<bool, UnabortableTransactionError> {
-        let quad = self.encode_quad(quad.into())?;
+        let quad = self.storage.encode_quad(quad.into())?;
         self.storage.insert(&quad)
     }
 
@@ -803,7 +784,7 @@ impl Transaction<'_> {
         &self,
         quad: impl Into<QuadRef<'a>>,
     ) -> Result<bool, UnabortableTransactionError> {
-        if let Some(quad) = self.get_encoded_quad(quad.into())? {
+        if let Some(quad) = self.storage.get_encoded_quad(quad.into())? {
             self.storage.remove(&quad)
         } else {
             Ok(false)
@@ -817,33 +798,11 @@ impl Transaction<'_> {
         &self,
         graph_name: impl Into<NamedOrBlankNodeRef<'a>>,
     ) -> Result<bool, UnabortableTransactionError> {
-        let graph_name = self.encode_named_or_blank_node(graph_name.into())?;
+        let graph_name = self.storage.encode_named_or_blank_node(graph_name.into())?;
         self.storage.insert_named_graph(graph_name)
     }
 }
 
-impl<'a> StrEncodingAware for &'a Transaction<'a> {
-    type Error = UnabortableTransactionError;
-}
-
-impl<'a> StrLookup for &'a Transaction<'a> {
-    fn get_str(&self, id: StrHash) -> Result<Option<String>, UnabortableTransactionError> {
-        self.storage.get_str(id)
-    }
-
-    fn get_str_id(&self, value: &str) -> Result<Option<StrHash>, UnabortableTransactionError> {
-        self.storage.get_str_id(value)
-    }
-}
-
-impl<'a> StrContainer for &'a Transaction<'a> {
-    fn insert_str(&self, value: &str) -> Result<StrHash, UnabortableTransactionError> {
-        let key = StrHash::new(value);
-        self.storage.insert_str(key, value)?;
-        Ok(key)
-    }
-}
-
 /// An iterator returning the quads contained in a [`Store`].
 pub struct QuadIter {
     inner: QuadIterInner,
@@ -864,7 +823,7 @@ impl Iterator for QuadIter {
     fn next(&mut self) -> Option<Result<Quad, io::Error>> {
         match &mut self.inner {
             QuadIterInner::Quads { iter, store } => Some(match iter.next()? {
-                Ok(quad) => store.decode_quad(&quad).map_err(|e| e.into()),
+                Ok(quad) => store.storage.decode_quad(&quad).map_err(|e| e.into()),
                 Err(error) => Err(error),
             }),
             QuadIterInner::Error(iter) => iter.next().map(Err),
@@ -884,9 +843,9 @@ impl Iterator for GraphNameIter {
 
     fn next(&mut self) -> Option<Result<NamedOrBlankNode, io::Error>> {
         Some(
-            self.iter
-                .next()?
-                .and_then(|graph_name| Ok(self.store.decode_named_or_blank_node(graph_name)?)),
+            self.iter.next()?.and_then(|graph_name| {
+                Ok(self.store.storage.decode_named_or_blank_node(graph_name)?)
+            }),
         )
     }