diff --git a/src/blob/mod.rs b/src/blob/mod.rs
index 6d39562b4..7b404f3ce 100644
--- a/src/blob/mod.rs
+++ b/src/blob/mod.rs
@@ -15,6 +15,8 @@ use std::{io, fmt, mem};
 use fst::Map;
 use uuid::Uuid;
 use rocksdb::rocksdb::{DB, Snapshot};
+use serde::ser::{Serialize, Serializer, SerializeTuple};
+use serde::de::{self, Deserialize, Deserializer, SeqAccess, Visitor};
 
 use crate::index::identifier::Identifier;
 use crate::data::DocIndexes;
@@ -33,6 +35,65 @@ impl Blob {
     }
 }
 
+impl Serialize for Blob {
+    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
+        match self {
+            Blob::Positive(blob) => {
+                let mut tuple = serializer.serialize_tuple(2)?;
+                tuple.serialize_element(&Sign::Positive)?;
+                tuple.serialize_element(&blob)?;
+                tuple.end()
+            },
+            Blob::Negative(blob) => {
+                let mut tuple = serializer.serialize_tuple(2)?;
+                tuple.serialize_element(&Sign::Negative)?;
+                tuple.serialize_element(&blob)?;
+                tuple.end()
+            },
+        }
+    }
+}
+
+impl<'de> Deserialize<'de> for Blob {
+    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Blob, D::Error> {
+        struct TupleVisitor;
+
+        impl<'de> Visitor<'de> for TupleVisitor {
+            type Value = Blob;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("a Blob struct")
+            }
+
+            #[inline]
+            fn visit_seq<A: SeqAccess<'de>>(self, mut seq: A) -> Result<Self::Value, A::Error> {
+                let sign = match seq.next_element()? {
+                    Some(value) => value,
+                    None => return Err(de::Error::invalid_length(0, &self)),
+                };
+                match sign {
+                    Sign::Positive => {
+                        let blob = match seq.next_element()? {
+                            Some(value) => value,
+                            None => return Err(de::Error::invalid_length(1, &self)),
+                        };
+                        Ok(Blob::Positive(blob))
+                    },
+                    Sign::Negative => {
+                        let blob = match seq.next_element()? {
+                            Some(value) => value,
+                            None => return Err(de::Error::invalid_length(1, &self)),
+                        };
+                        Ok(Blob::Negative(blob))
+                    },
+                }
+            }
+        }
+
+        deserializer.deserialize_tuple(2, TupleVisitor)
+    }
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub enum Sign {
     Positive,
diff --git a/src/blob/negative_blob.rs b/src/blob/negative_blob.rs
index 0226b5ae5..19ff5d026 100644
--- a/src/blob/negative_blob.rs
+++ b/src/blob/negative_blob.rs
@@ -1,9 +1,11 @@
+use std::io::{Read, Write};
 use std::error::Error;
 use std::path::Path;
-use std::io::Write;
 
 use crate::DocumentId;
 use crate::data::{DocIds, DocIdsBuilder};
+use serde::ser::{Serialize, Serializer};
+use serde::de::{self, Deserialize, Deserializer};
 
 pub struct NegativeBlob {
     doc_ids: DocIds,
@@ -31,6 +33,19 @@ impl NegativeBlob {
     }
 }
 
+impl Serialize for NegativeBlob {
+    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
+        self.doc_ids.serialize(serializer)
+    }
+}
+
+impl<'de> Deserialize<'de> for NegativeBlob {
+    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<NegativeBlob, D::Error> {
+        let bytes = Vec::deserialize(deserializer)?;
+        NegativeBlob::from_bytes(bytes).map_err(de::Error::custom)
+    }
+}
+
 pub struct NegativeBlobBuilder<W> {
     doc_ids: DocIdsBuilder<W>,
 }
diff --git a/src/blob/positive_blob.rs b/src/blob/positive_blob.rs
index ac1e85d46..29966cd68 100644
--- a/src/blob/positive_blob.rs
+++ b/src/blob/positive_blob.rs
@@ -1,11 +1,14 @@
+use std::io::{Read, Write};
 use std::error::Error;
 use std::path::Path;
-use std::io::Write;
+use std::fmt;
 
 use fst::{Map, MapBuilder};
 
 use crate::DocIndex;
 use crate::data::{DocIndexes, DocIndexesBuilder};
+use serde::ser::{Serialize, Serializer, SerializeTuple};
+use serde::de::{self, Deserialize, Deserializer, SeqAccess, Visitor};
 
 pub struct PositiveBlob {
     map: Map,
@@ -45,6 +48,52 @@ impl PositiveBlob {
     }
 }
 
+impl Serialize for PositiveBlob {
+    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
+        let mut tuple = serializer.serialize_tuple(2)?;
+        tuple.serialize_element(&self.map.as_fst().to_vec())?;
+        tuple.serialize_element(&self.indexes)?;
+        tuple.end()
+    }
+}
+
+impl<'de> Deserialize<'de> for PositiveBlob {
+    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<PositiveBlob, D::Error> {
+        struct TupleVisitor;
+
+        impl<'de> Visitor<'de> for TupleVisitor {
+            type Value = PositiveBlob;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("a PositiveBlob struct")
+            }
+
+            #[inline]
+            fn visit_seq<A: SeqAccess<'de>>(self, mut seq: A) -> Result<Self::Value, A::Error> {
+                let map = match seq.next_element()? {
+                    Some(bytes) => match Map::from_bytes(bytes) {
+                        Ok(value) => value,
+                        Err(err) => return Err(de::Error::custom(err)),
+                    },
+                    None => return Err(de::Error::invalid_length(0, &self)),
+                };
+
+                let indexes = match seq.next_element()? {
+                    Some(bytes) => match DocIndexes::from_bytes(bytes) {
+                        Ok(value) => value,
+                        Err(err) => return Err(de::Error::custom(err)),
+                    },
+                    None => return Err(de::Error::invalid_length(1, &self)),
+                };
+
+                Ok(PositiveBlob { map, indexes })
+            }
+        }
+
+        deserializer.deserialize_tuple(2, TupleVisitor)
+    }
+}
+
 pub struct PositiveBlobBuilder<W, X> {
     map: W,
     indexes: DocIndexesBuilder<X>,
diff --git a/src/data/doc_ids.rs b/src/data/doc_ids.rs
index 4907a29f8..168ca0b46 100644
--- a/src/data/doc_ids.rs
+++ b/src/data/doc_ids.rs
@@ -7,31 +7,32 @@ use std::{io, mem};
 
 use byteorder::{NativeEndian, WriteBytesExt};
 use fst::raw::MmapReadOnly;
+use serde::ser::{Serialize, Serializer};
 
 use crate::DocumentId;
 use crate::data::Data;
 
 #[derive(Clone)]
 pub struct DocIds {
-    doc_ids: Data,
+    data: Data,
 }
 
 impl DocIds {
     pub unsafe fn from_path<P: AsRef<Path>>(path: P) -> io::Result<Self> {
         let mmap = MmapReadOnly::open_path(path)?;
-        let doc_ids = Data::Mmap(mmap);
-        Ok(DocIds { doc_ids })
+        let data = Data::Mmap(mmap);
+        Ok(DocIds { data })
     }
 
     pub fn from_bytes(vec: Vec<u8>) -> Result<Self, Box<Error>> {
         // FIXME check if modulo DocumentId
         let len = vec.len();
-        let doc_ids = Data::Shared {
+        let data = Data::Shared {
             vec: Arc::new(vec),
             offset: 0,
             len: len
         };
-        Ok(DocIds { doc_ids })
+        Ok(DocIds { data })
     }
 
     pub fn contains(&self, doc: DocumentId) -> bool {
@@ -40,13 +41,19 @@ impl DocIds {
     }
 
     pub fn doc_ids(&self) -> &[DocumentId] {
-        let slice = &self.doc_ids;
+        let slice = &self.data;
         let ptr = slice.as_ptr() as *const DocumentId;
         let len = slice.len() / mem::size_of::<DocumentId>();
         unsafe { from_raw_parts(ptr, len) }
     }
 }
 
+impl Serialize for DocIds {
+    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
+        self.data.as_ref().serialize(serializer)
+    }
+}
+
 pub struct DocIdsBuilder<W> {
     doc_ids: BTreeSet<DocumentId>, // TODO: prefer a linked-list
     wrt: W,
diff --git a/src/data/doc_indexes.rs b/src/data/doc_indexes.rs
index bb0cea837..97222b205 100644
--- a/src/data/doc_indexes.rs
+++ b/src/data/doc_indexes.rs
@@ -8,6 +8,7 @@ use std::mem;
 
 use fst::raw::MmapReadOnly;
 use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
+use serde::ser::{Serialize, Serializer, SerializeTuple};
 
 use crate::DocIndex;
 use crate::data::Data;
@@ -84,6 +85,15 @@ impl DocIndexes {
     }
 }
 
+impl Serialize for DocIndexes {
+    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
+        let mut tuple = serializer.serialize_tuple(2)?;
+        tuple.serialize_element(self.ranges.as_ref())?;
+        tuple.serialize_element(self.indexes.as_ref())?;
+        tuple.end()
+    }
+}
+
 pub struct DocIndexesBuilder<W> {
     keys: BTreeMap<String, u64>,
     indexes: Vec<Vec<DocIndex>>,
diff --git a/src/data/mod.rs b/src/data/mod.rs
index 0f16621fb..ca9816fa3 100644
--- a/src/data/mod.rs
+++ b/src/data/mod.rs
@@ -23,6 +23,12 @@ impl Deref for Data {
     type Target = [u8];
 
     fn deref(&self) -> &Self::Target {
+        self.as_ref()
+    }
+}
+
+impl AsRef<[u8]> for Data {
+    fn as_ref(&self) -> &[u8] {
         match self {
             Data::Shared { vec, offset, len } => {
                 &vec[*offset..offset + len]
diff --git a/src/index/mod.rs b/src/index/mod.rs
index f03c8848e..9de25f476 100644
--- a/src/index/mod.rs
+++ b/src/index/mod.rs
@@ -22,7 +22,7 @@ use crate::{DocIndex, DocumentId};
 use crate::index::schema::Schema;
 use crate::index::update::Update;
 use crate::index::identifier::Identifier;
-use crate::blob::{PositiveBlobBuilder, BlobInfo, Sign, Blob, blobs_from_blob_infos};
+use crate::blob::{PositiveBlobBuilder, PositiveBlob, BlobInfo, Sign, Blob, blobs_from_blob_infos};
 use crate::tokenizer::{TokenizerBuilder, DefaultBuilder, Tokenizer};
 use crate::rank::{criterion, Config, RankedStream};
 use crate::automaton;
@@ -35,6 +35,45 @@ fn simple_vec_append(key: &[u8], value: Option<&[u8]>, operands: &mut MergeOpera
     output
 }
 
+pub struct MergeBuilder {
+    blobs: Vec<Blob>,
+}
+
+impl MergeBuilder {
+    pub fn new() -> MergeBuilder {
+        MergeBuilder { blobs: Vec::new() }
+    }
+
+    pub fn push(&mut self, blob: Blob) {
+        if blob.sign() == Sign::Negative && self.blobs.is_empty() { return }
+        self.blobs.push(blob);
+    }
+
+    pub fn merge(self) -> PositiveBlob {
+        unimplemented!()
+    }
+}
+
+fn merge_indexes(key: &[u8], existing_value: Option<&[u8]>, operands: &mut MergeOperands) -> Vec<u8> {
+    if key != b"data-index" { panic!("The merge operator only allow \"data-index\" merging") }
+
+    let mut merge_builder = MergeBuilder::new();
+
+    if let Some(existing_value) = existing_value {
+        let base: PositiveBlob = bincode::deserialize(existing_value).unwrap(); // FIXME what do we do here ?
+        merge_builder.push(Blob::Positive(base));
+    }
+
+    for bytes in operands {
+        let blob: Blob = bincode::deserialize(bytes).unwrap();
+        merge_builder.push(blob);
+    }
+
+    let blob = merge_builder.merge();
+    // blob.to_vec()
+    unimplemented!()
+}
+
 pub struct Index {
     database: rocksdb::DB,
 }