diff --git a/src/backup.rs b/src/backup.rs
index 1d0e130..8c46379 100644
--- a/src/backup.rs
+++ b/src/backup.rs
@@ -9,7 +9,7 @@ use walkdir::WalkDir;
 
 use crate::error::BakareError;
 use crate::repository::Repository;
-use crate::Version;
+use crate::ItemVersion;
 
 pub struct Engine<'a> {
     source_path: &'a Path,
diff --git a/src/lib.rs b/src/lib.rs
index c3ade8b..77baec3 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -12,7 +12,9 @@ pub mod source;
 
 pub mod repository;
 
-pub struct Version(String);
+pub struct ItemVersion(String);
 
-struct Index {
+pub struct IndexVersion;
+struct IndexViewReadonly {
+   index_version: IndexVersion
 }
diff --git a/src/repository.rs b/src/repository.rs
index 8d9606a..d90e3cc 100644
--- a/src/repository.rs
+++ b/src/repository.rs
@@ -6,22 +6,30 @@ use std::path::Path;
 use walkdir::DirEntry;
 
 use crate::error::BakareError;
-use crate::Version;
-use crate::Index;
+use crate::ItemVersion;
+use crate::IndexViewReadonly;
+use crate::IndexVersion;
 
 /// represents a place where backup is stored an can be restored from.
 /// right now only on-disk directory storage is supported
+/// repository always knows the newest version of the index and is responsible for syncing the index to disk
+/// and making sure that different threads can access index in parallel
 pub struct Repository<'a> {
     /// absolute path to where the repository is stored on disk
     path: &'a Path,
-    index: Index
+    index: IndexViewReadonly,
+    newest_index_version: IndexVersion
 }
 
 pub struct RepositoryItem {
-    version: Version
+    version: ItemVersion
 }
 
-pub struct RepositoryIterator;
+
+pub struct RepositoryIterator {
+    version: IndexVersion,
+    index: IndexViewReadonly
+}
 
 impl<'a> Iterator for RepositoryIterator {
     type Item = RepositoryItem;
@@ -32,7 +40,7 @@ impl<'a> Iterator for RepositoryIterator {
 }
 
 impl RepositoryItem {
-    pub fn version(&self) -> &Version {
+    pub fn version(&self) -> &ItemVersion {
         &self.version
     }
 }
@@ -41,11 +49,11 @@ impl<'a> Repository<'a> {
     pub fn open(path: &Path) -> Result<Repository, BakareError> {
         // TODO open index from file
 
-        Ok(Repository { path, index: Index {} })
+        Ok(Repository { path, index: IndexViewReadonly {} })
     }
 
     pub fn iter(&self) -> RepositoryIterator {
-        unimplemented!()
+
     }
 
     pub fn store(&self, source_path: &Path) -> Result<(), BakareError> {
@@ -70,7 +78,7 @@ impl<'a> Repository<'a> {
         unimplemented!()
     }
 
-    pub fn newest_version_for(&self, source_path: &Path) -> Result<Version, BakareError> {
+    pub fn newest_version_for(&self, source_path: &Path) -> Result<ItemVersion, BakareError> {
         unimplemented!()
     }
 
diff --git a/src/restore.rs b/src/restore.rs
index 4c7845f..8c9fe58 100644
--- a/src/restore.rs
+++ b/src/restore.rs
@@ -8,7 +8,7 @@ use walkdir::WalkDir;
 
 use crate::error::BakareError;
 use crate::repository::Repository;
-use crate::Version;
+use crate::ItemVersion;
 use crate::repository::RepositoryItem;
 
 pub struct Engine<'a> {
@@ -32,7 +32,7 @@ impl<'a> Engine<'a> {
         unimplemented!()
     }
 
-    pub fn restore_as_of_version(&self, item: &RepositoryItem, version: &Version) -> Result<(), BakareError> {
+    pub fn restore_as_of_version(&self, item: &RepositoryItem, version: &ItemVersion) -> Result<(), BakareError> {
         unimplemented!()
     }