diff --git a/src/core/directory.rs b/src/core/directory.rs
index 14b604568..212f7dc76 100644
--- a/src/core/directory.rs
+++ b/src/core/directory.rs
@@ -5,44 +5,53 @@ use self::memmap::{Mmap, Protection};
 use std::path::PathBuf;
 use std::fs::File;
 use std::io;
+use std::rc::Rc;
 
 #[derive(Clone, Debug)]
-struct SegmentId(String);
+pub struct SegmentId(String);
 
-struct IndexDirectory {
-    index_path: PathBuf,
+pub trait Dir {
+    fn get_file(&self, segment_id: &SegmentId, component: SegmentComponent) -> Result<File, io::Error>;
 }
 
-impl IndexDirectory {
+#[derive(Clone)]
+pub struct Directory {
+    dir: Rc<Dir>,
+}
 
-    pub fn for_path(path: PathBuf)-> IndexDirectory {
-        IndexDirectory {
-            index_path: path,
-        }
-    }
-
-    pub fn read_segment(&self, segment_id: &SegmentId) -> SegmentDirectory {
-        SegmentDirectory {
-            index_path: self.index_path.clone(),
+impl Directory {
+    fn segment(&self, segment_id: &SegmentId) -> Segment {
+        Segment {
+            directory: self.dir.clone(),
             segment_id: segment_id.clone()
         }
     }
 
-    
-
+    pub fn open(path_str: &str) -> Directory {
+        let path = PathBuf::from(path_str);
+        Directory {
+            dir: Rc::new(FileDirectory::for_path(path)),
+        }
+    }
 }
 
-enum SegmentComponent {
+impl Dir for Directory {
+    fn get_file(&self, segment_id: &SegmentId, component: SegmentComponent) -> Result<File, io::Error> {
+        self.dir.get_file(segment_id, component)
+    }
+}
+
+pub enum SegmentComponent {
     POSTINGS,
     POSITIONS,
 }
 
-struct SegmentDirectory {
-    index_path: PathBuf,
+pub struct Segment {
+    directory: Rc<Dir>,
     segment_id: SegmentId,
 }
 
-impl SegmentDirectory {
+impl Segment {
 
     fn path_suffix(component: SegmentComponent)-> &'static str {
         match component {
@@ -52,11 +61,7 @@ impl SegmentDirectory {
     }
 
     fn get_file(&self, component: SegmentComponent) -> Result<File, io::Error> {
-        let mut res = self.index_path.clone();
-        let SegmentId(ref segment_id_str) = self.segment_id;
-        let filename = String::new() + segment_id_str + "." + SegmentDirectory::path_suffix(component);
-        res.push(filename);
-        File::open(res)
+        self.directory.get_file(&self.segment_id, component)
     }
 
     pub fn open(&self, component: SegmentComponent) -> Result<Mmap, io::Error> {
@@ -64,3 +69,26 @@ impl SegmentDirectory {
         Mmap::open(&file, Protection::Read)
     }
 }
+
+
+pub struct FileDirectory {
+    index_path: PathBuf,
+}
+
+impl FileDirectory {
+    pub fn for_path(path: PathBuf)-> FileDirectory {
+        FileDirectory {
+            index_path: path,
+        }
+    }
+}
+
+impl Dir for FileDirectory {
+    fn get_file(&self, segment_id: &SegmentId, component: SegmentComponent) -> Result<File, io::Error> {
+        let mut res = self.index_path.clone();
+        let SegmentId(ref segment_id_str) = *segment_id;
+        let filename = String::new() + segment_id_str + "." + Segment::path_suffix(component);
+        res.push(filename);
+        File::open(res)
+    }
+}
diff --git a/src/core/schema.rs b/src/core/schema.rs
index 0d8ea85ee..52797bbbe 100644
--- a/src/core/schema.rs
+++ b/src/core/schema.rs
@@ -1,6 +1,3 @@
-use std::collections::HashMap;
-use std::sync::{Mutex, MutexGuard};
-
 #[derive(Clone,Debug,PartialEq,PartialOrd,Eq,Hash)]
 pub struct Field(pub &'static str);
 
diff --git a/src/core/writer.rs b/src/core/writer.rs
index a04361071..a5e4ddca7 100644
--- a/src/core/writer.rs
+++ b/src/core/writer.rs
@@ -1,8 +1,8 @@
 
 use std::io;
 use core::schema::Document;
-use core::schema::Term;
-use core::schema::Field ;
+use core::schema::Field;
+use core::directory::Directory;
 use core::analyzer::tokenize;
 use std::collections::{HashMap, BTreeMap};
 use core::DocId;
@@ -57,14 +57,16 @@ impl FieldWriter {
 pub struct IndexWriter {
     max_doc: usize,
     term_writers: HashMap<Field, FieldWriter>,
+	directory: Directory,
 }
 
 impl IndexWriter {
 
-    pub fn new() -> IndexWriter {
-        IndexWriter {
+    pub fn open(directory: &Directory) -> IndexWriter {
+		IndexWriter {
             max_doc: 0,
             term_writers: HashMap::new(),
+			directory: (*directory).clone(),
         }
     }
 
diff --git a/tests/core.rs b/tests/core.rs
index 7214ab6df..0a481bab5 100644
--- a/tests/core.rs
+++ b/tests/core.rs
@@ -6,6 +6,7 @@ use parici::core::postings::{VecPostings, intersection};
 use parici::core::postings::Postings;
 use parici::core::analyzer::tokenize;
 use parici::core::writer::IndexWriter;
+use parici::core::directory::Directory;
 use parici::core::schema::{Field, Document};
 
 #[test]
@@ -25,7 +26,8 @@ fn test_tokenizer() {
 
 #[test]
 fn test_indexing() {
-    let mut index_writer = IndexWriter::new();
+    let directory = Directory::open("toto");
+    let mut index_writer = IndexWriter::open(&directory);
     let mut doc = Document::new();
     doc.set(Field("text"), &String::from("toto"));
     index_writer.add(doc);