diff --git a/edm4eic.yaml b/edm4eic.yaml
index 73e94d9..2288d22 100644
--- a/edm4eic.yaml
+++ b/edm4eic.yaml
@@ -356,6 +356,8 @@ datatypes:
       - float             timeError         // Error on the time
       - float             edep              // Energy deposit in this hit [GeV]
       - float             edepError         // Error on the energy deposit [GeV]
+    OneToOneRelations:
+      - edm4eic::RawTrackerHit rawHit       // reference to raw hits. should be one to one. 
 
   edm4eic::Measurement2D:
     Description: "2D measurement (on an arbitrary surface)"
@@ -371,6 +373,32 @@ datatypes:
       - edm4eic::TrackerHit hits            // Hits in this measurement (single or clustered)
 
       
+
+    
+  edm4eic::TrackParameters:
+    Description: "ACTS Bound Track parameters"
+    Author: "W. Armstrong, S. Joosten, J. Osborn"
+    Members:
+      - int32_t              type              // Type of track parameters (-1/seed, 0/head, ...)
+      - uint64_t             surface           // Surface for bound parameters (geometryID)
+      - edm4hep::Vector2f    loc               // 2D location on surface
+      - float                theta             // Track polar angle [rad]
+      - float                phi               // Track azimuthal angle [rad]
+      - float                qOverP            // [e/GeV]
+      - float                time              // Track time [ns] 
+      - int32_t              pdg               // pdg pid for these parameters
+      - edm4eic::Cov6f       covariance        // Full covariance in basis [l0,l1,theta,phi,q/p,t]
+
+  edm4eic::TrackSeed:
+    Description: "save seed info from the realistic seed finder"
+    Author: "S. Li"
+    Members:
+      - edm4hep::Vector3f  perigee   // vector to create the perigee (line surface)
+    OneToManyRelations:
+      - edm4eic::TrackerHit triplet  // three tracker hits used to form the seed 
+    oneToOneRelations:
+      - edm4eic::TrackParameters seedParams  // initial track parameters from fitting the triplet
+
   edm4eic::Trajectory:
     Description: "Raw trajectory from the tracking algorithm. What is called hit here is 2d measurement indeed."
     Author: "S. Joosten, S. Li"
@@ -386,20 +414,8 @@ datatypes:
       - float             outlierChi2       // Chi2 for each of the outliers
     OneToManyRelations:
       - edm4eic::TrackParameters trackParameters // Associated track parameters, if any
-  
-  edm4eic::TrackParameters:
-    Description: "ACTS Bound Track parameters"
-    Author: "W. Armstrong, S. Joosten, J. Osborn"
-    Members:
-      - int32_t              type              // Type of track parameters (-1/seed, 0/head, ...)
-      - uint64_t             surface           // Surface for bound parameters (geometryID)
-      - edm4hep::Vector2f    loc               // 2D location on surface
-      - float                theta             // Track polar angle [rad]
-      - float                phi               // Track azimuthal angle [rad]
-      - float                qOverP            // [e/GeV]
-      - float                time              // Track time [ns] 
-      - int32_t              pdg               // pdg pid for these parameters
-      - edm4eic::Cov6f       covariance        // Full covariance in basis [l0,l1,theta,phi,q/p,t]
+    OneToOneRelations:
+      - edm4eic::TrackSeed seed // Associated seed
 
 
   edm4eic::Track:
@@ -526,8 +542,21 @@ datatypes:
     Description: "Association between a RawTrackerHit and a SimTrackerHit"
     Author: "C. Dilks, W. Deconinck"
     Members:
-      - float                 weight        // weight of this association
+      - float                 weight         // weight of this association
+    OneToOneRelations:
+      - edm4eic::RawTrackerHit rawHit        // reference to the digitized hit
+    OneToManyRelations:
+      - edm4hep::SimTrackerHit simHits       // reference to the simulated hits
+
+
+  edm4eic::MCParticleRecoHitAssociation:
+    Description: "Association between a TrackHit and MCParticles. One tracker hit can be linked to multiple raw hits hence multiple particles"
+    Author : "S. Li"
+    VectorMembers:
+      - uint32_t          simIDs             // Index of corresponding MCParticles (position in MCParticles array)
+      - float             weights            // weight of this association
     OneToOneRelations:
-     - edm4eic::RawTrackerHit rawHit        // reference to the digitized hit
+      - edm4eic::TrackerHit trackHit        // reference to the hit
     OneToManyRelations:
-     - edm4hep::SimTrackerHit simHits       // reference to the simulated hits
+      - edm4hep::MCParticle mcParticles     // reference to the Monte-Carlo particle
+