diff --git a/app/app.go b/app/app.go
index 22ea65708..90f6c88a3 100644
--- a/app/app.go
+++ b/app/app.go
@@ -575,7 +575,7 @@ func wireValidatorMock(conf Config, pubshares []eth2p0.BLSPubKey, sched core.Sch
 	signer := validatormock.NewSigner(secrets...)
 
 	// Trigger validatormock when scheduler triggers new slot.
-	sched.Subscribe(func(ctx context.Context, duty core.Duty, _ core.FetchArgSet) error {
+	sched.Subscribe(func(ctx context.Context, duty core.Duty, _ core.DutyDefinitionSet) error {
 		ctx = log.WithTopic(ctx, "vmock")
 		go func() {
 			addr := "http://" + conf.ValidatorAPIAddr
diff --git a/core/dutydefinition.go b/core/dutydefinition.go
index 368901766..036a8d28e 100644
--- a/core/dutydefinition.go
+++ b/core/dutydefinition.go
@@ -22,8 +22,8 @@ import (
 )
 
 var (
-	_ FetchArg = AttesterDefinition{}
-	_ FetchArg = ProposerDefinition{}
+	_ DutyDefinition = AttesterDefinition{}
+	_ DutyDefinition = ProposerDefinition{}
 )
 
 // NewAttesterDefinition is a convenience function that returns a new attester definition.
@@ -31,13 +31,13 @@ func NewAttesterDefinition(duty *eth2v1.AttesterDuty) AttesterDefinition {
 	return AttesterDefinition{AttesterDuty: *duty}
 }
 
-// AttesterDefinition defines an attester duty. It implements FetchArg.
+// AttesterDefinition defines an attester duty. It implements DutyDefinition.
 // Note the slight rename from Duty to Definition to avoid overloading the term Duty.
 type AttesterDefinition struct {
 	eth2v1.AttesterDuty
 }
 
-func (d AttesterDefinition) Clone() (FetchArg, error) {
+func (d AttesterDefinition) Clone() (DutyDefinition, error) {
 	duty := new(eth2v1.AttesterDuty)
 	err := cloneJSONMarshaler(&d.AttesterDuty, duty)
 	if err != nil {
@@ -56,13 +56,13 @@ func NewProposerDefinition(duty *eth2v1.ProposerDuty) ProposerDefinition {
 	return ProposerDefinition{ProposerDuty: *duty}
 }
 
-// ProposerDefinition defines a block proposer duty. It implements FetchArg.
+// ProposerDefinition defines a block proposer duty. It implements DutyDefinition.
 // Note the slight rename from Duty to Definition to avoid overloading the term Duty.
 type ProposerDefinition struct {
 	eth2v1.ProposerDuty
 }
 
-func (d ProposerDefinition) Clone() (FetchArg, error) {
+func (d ProposerDefinition) Clone() (DutyDefinition, error) {
 	duty := new(eth2v1.ProposerDuty)
 	err := cloneJSONMarshaler(&d.ProposerDuty, duty)
 	if err != nil {
diff --git a/core/fetcher/fetcher.go b/core/fetcher/fetcher.go
index 27f6e3e3f..2b94d917c 100644
--- a/core/fetcher/fetcher.go
+++ b/core/fetcher/fetcher.go
@@ -58,7 +58,7 @@ func (f *Fetcher) Subscribe(fn func(context.Context, core.Duty, core.UnsignedDat
 }
 
 // Fetch triggers fetching of a proposed duty data set.
-func (f *Fetcher) Fetch(ctx context.Context, duty core.Duty, argSet core.FetchArgSet) error {
+func (f *Fetcher) Fetch(ctx context.Context, duty core.Duty, defSet core.DutyDefinitionSet) error {
 	var (
 		unsignedSet core.UnsignedDataSet
 		err         error
@@ -66,12 +66,12 @@ func (f *Fetcher) Fetch(ctx context.Context, duty core.Duty, argSet core.FetchAr
 
 	switch duty.Type {
 	case core.DutyProposer:
-		unsignedSet, err = f.fetchProposerData(ctx, duty.Slot, argSet)
+		unsignedSet, err = f.fetchProposerData(ctx, duty.Slot, defSet)
 		if err != nil {
 			return errors.Wrap(err, "fetch proposer data")
 		}
 	case core.DutyAttester:
-		unsignedSet, err = f.fetchAttesterData(ctx, duty.Slot, argSet)
+		unsignedSet, err = f.fetchAttesterData(ctx, duty.Slot, defSet)
 		if err != nil {
 			return errors.Wrap(err, "fetch attester data")
 		}
@@ -100,14 +100,14 @@ func (f *Fetcher) RegisterAggSigDB(fn func(context.Context, core.Duty, core.PubK
 }
 
 // fetchAttesterData returns the fetched attestation data set for committees and validators in the arg set.
-func (f *Fetcher) fetchAttesterData(ctx context.Context, slot int64, argSet core.FetchArgSet,
+func (f *Fetcher) fetchAttesterData(ctx context.Context, slot int64, defSet core.DutyDefinitionSet,
 ) (core.UnsignedDataSet, error) {
 	// We may have multiple validators in the same committee, use the same attestation data in that case.
 	dataByCommIdx := make(map[eth2p0.CommitteeIndex]*eth2p0.AttestationData)
 
 	resp := make(core.UnsignedDataSet)
-	for pubkey, fetchArg := range argSet {
-		attDuty, ok := fetchArg.(core.AttesterDefinition)
+	for pubkey, def := range defSet {
+		attDuty, ok := def.(core.AttesterDefinition)
 		if !ok {
 			return nil, errors.New("invalid attester definition")
 		}
@@ -134,9 +134,9 @@ func (f *Fetcher) fetchAttesterData(ctx context.Context, slot int64, argSet core
 	return resp, nil
 }
 
-func (f *Fetcher) fetchProposerData(ctx context.Context, slot int64, argSet core.FetchArgSet) (core.UnsignedDataSet, error) {
+func (f *Fetcher) fetchProposerData(ctx context.Context, slot int64, defSet core.DutyDefinitionSet) (core.UnsignedDataSet, error) {
 	resp := make(core.UnsignedDataSet)
-	for pubkey := range argSet {
+	for pubkey := range defSet {
 		// Fetch previously aggregated randao reveal from AggSigDB
 		dutyRandao := core.Duty{
 			Slot: slot,
diff --git a/core/fetcher/fetcher_test.go b/core/fetcher/fetcher_test.go
index e574150b6..79e190149 100644
--- a/core/fetcher/fetcher_test.go
+++ b/core/fetcher/fetcher_test.go
@@ -61,7 +61,7 @@ func TestFetchAttester(t *testing.T) {
 		CommitteesAtSlot: notZero,
 	}
 
-	argSet := core.FetchArgSet{
+	defSet := core.DutyDefinitionSet{
 		pubkeysByIdx[vIdxA]: core.NewAttesterDefinition(&dutyA),
 		pubkeysByIdx[vIdxB]: core.NewAttesterDefinition(&dutyB),
 	}
@@ -89,7 +89,7 @@ func TestFetchAttester(t *testing.T) {
 		return nil
 	})
 
-	err = fetch.Fetch(ctx, duty, argSet)
+	err = fetch.Fetch(ctx, duty, defSet)
 	require.NoError(t, err)
 }
 
@@ -115,7 +115,7 @@ func TestFetchProposer(t *testing.T) {
 		Slot:           slot,
 		ValidatorIndex: vIdxB,
 	}
-	argSet := core.FetchArgSet{
+	defSet := core.DutyDefinitionSet{
 		pubkeysByIdx[vIdxA]: core.NewProposerDefinition(&dutyA),
 		pubkeysByIdx[vIdxB]: core.NewProposerDefinition(&dutyB),
 	}
@@ -156,7 +156,7 @@ func TestFetchProposer(t *testing.T) {
 		return nil
 	})
 
-	err = fetch.Fetch(ctx, duty, argSet)
+	err = fetch.Fetch(ctx, duty, defSet)
 	require.NoError(t, err)
 }
 
diff --git a/core/interfaces.go b/core/interfaces.go
index ce22e1542..136d79cc2 100644
--- a/core/interfaces.go
+++ b/core/interfaces.go
@@ -25,16 +25,16 @@ import (
 // Scheduler triggers the start of a duty workflow.
 type Scheduler interface {
 	// Subscribe registers a callback for fetching a duty.
-	Subscribe(func(context.Context, Duty, FetchArgSet) error)
+	Subscribe(func(context.Context, Duty, DutyDefinitionSet) error)
 
-	// GetDuty returns the argSet for a duty if resolved already.
-	GetDuty(context.Context, Duty) (FetchArgSet, error)
+	// GetDutyDefinition returns the definition set for a duty if already resolved.
+	GetDutyDefinition(context.Context, Duty) (DutyDefinitionSet, error)
 }
 
 // Fetcher fetches proposed unsigned duty data.
 type Fetcher interface {
 	// Fetch triggers fetching of a proposed duty data set.
-	Fetch(context.Context, Duty, FetchArgSet) error
+	Fetch(context.Context, Duty, DutyDefinitionSet) error
 
 	// Subscribe registers a callback for proposed unsigned duty data sets.
 	Subscribe(func(context.Context, Duty, UnsignedDataSet) error)
@@ -85,8 +85,8 @@ type ValidatorAPI interface {
 	// RegisterPubKeyByAttestation registers a function to query validator by attestation.
 	RegisterPubKeyByAttestation(func(ctx context.Context, slot, commIdx, valCommIdx int64) (PubKey, error))
 
-	// RegisterGetDutyFunc registers a function to query duty data.
-	RegisterGetDutyFunc(func(context.Context, Duty) (FetchArgSet, error))
+	// RegisterGetDutyDefinition registers a function to query duty definitions.
+	RegisterGetDutyDefinition(func(context.Context, Duty) (DutyDefinitionSet, error))
 
 	// RegisterParSigDB registers a function to store partially signed data sets.
 	RegisterParSigDB(func(context.Context, Duty, ParSignedDataSet) error)
@@ -146,9 +146,9 @@ type Broadcaster interface {
 // wireFuncs defines the core workflow components as a list input and output functions
 // instead as interfaces, since functions are easier to wrap than interfaces.
 type wireFuncs struct {
-	SchedulerSubscribe              func(func(context.Context, Duty, FetchArgSet) error)
-	SchedulerGetDuty                func(context.Context, Duty) (FetchArgSet, error)
-	FetcherFetch                    func(context.Context, Duty, FetchArgSet) error
+	SchedulerSubscribe              func(func(context.Context, Duty, DutyDefinitionSet) error)
+	SchedulerGetDutyDefinition      func(context.Context, Duty) (DutyDefinitionSet, error)
+	FetcherFetch                    func(context.Context, Duty, DutyDefinitionSet) error
 	FetcherSubscribe                func(func(context.Context, Duty, UnsignedDataSet) error)
 	FetcherRegisterAggSigDB         func(func(context.Context, Duty, PubKey) (SignedData, error))
 	ConsensusPropose                func(context.Context, Duty, UnsignedDataSet) error
@@ -159,7 +159,7 @@ type wireFuncs struct {
 	DutyDBPubKeyByAttestation       func(ctx context.Context, slot, commIdx, valCommIdx int64) (PubKey, error)
 	VAPIRegisterAwaitAttestation    func(func(ctx context.Context, slot, commIdx int64) (*eth2p0.AttestationData, error))
 	VAPIRegisterAwaitBeaconBlock    func(func(ctx context.Context, slot int64) (*spec.VersionedBeaconBlock, error))
-	VAPIRegisterGetDutyFunc         func(func(context.Context, Duty) (FetchArgSet, error))
+	VAPIRegisterGetDutyDefinition   func(func(context.Context, Duty) (DutyDefinitionSet, error))
 	VAPIRegisterPubKeyByAttestation func(func(ctx context.Context, slot, commIdx, valCommIdx int64) (PubKey, error))
 	VAPIRegisterParSigDB            func(func(context.Context, Duty, ParSignedDataSet) error)
 	ParSigDBStoreInternal           func(context.Context, Duty, ParSignedDataSet) error
@@ -193,7 +193,7 @@ func Wire(sched Scheduler,
 ) {
 	w := wireFuncs{
 		SchedulerSubscribe:              sched.Subscribe,
-		SchedulerGetDuty:                sched.GetDuty,
+		SchedulerGetDutyDefinition:      sched.GetDutyDefinition,
 		FetcherFetch:                    fetch.Fetch,
 		FetcherSubscribe:                fetch.Subscribe,
 		FetcherRegisterAggSigDB:         fetch.RegisterAggSigDB,
@@ -205,7 +205,7 @@ func Wire(sched Scheduler,
 		DutyDBPubKeyByAttestation:       dutyDB.PubKeyByAttestation,
 		VAPIRegisterAwaitBeaconBlock:    vapi.RegisterAwaitBeaconBlock,
 		VAPIRegisterAwaitAttestation:    vapi.RegisterAwaitAttestation,
-		VAPIRegisterGetDutyFunc:         vapi.RegisterGetDutyFunc,
+		VAPIRegisterGetDutyDefinition:   vapi.RegisterGetDutyDefinition,
 		VAPIRegisterPubKeyByAttestation: vapi.RegisterPubKeyByAttestation,
 		VAPIRegisterParSigDB:            vapi.RegisterParSigDB,
 		ParSigDBStoreInternal:           parSigDB.StoreInternal,
@@ -231,7 +231,7 @@ func Wire(sched Scheduler,
 	w.ConsensusSubscribe(w.DutyDBStore)
 	w.VAPIRegisterAwaitBeaconBlock(w.DutyDBAwaitBeaconBlock)
 	w.VAPIRegisterAwaitAttestation(w.DutyDBAwaitAttestation)
-	w.VAPIRegisterGetDutyFunc(w.SchedulerGetDuty)
+	w.VAPIRegisterGetDutyDefinition(w.SchedulerGetDutyDefinition)
 	w.VAPIRegisterPubKeyByAttestation(w.DutyDBPubKeyByAttestation)
 	w.VAPIRegisterParSigDB(w.ParSigDBStoreInternal)
 	w.ParSigDBSubscribeInternal(w.ParSigExBroadcast)
diff --git a/core/retry.go b/core/retry.go
index 2fe0c2e09..3345f5681 100644
--- a/core/retry.go
+++ b/core/retry.go
@@ -25,7 +25,7 @@ import (
 func WithAsyncRetry(retryer *retry.Retryer[Duty]) WireOption {
 	return func(w *wireFuncs) {
 		clone := *w
-		w.FetcherFetch = func(ctx context.Context, duty Duty, set FetchArgSet) error {
+		w.FetcherFetch = func(ctx context.Context, duty Duty, set DutyDefinitionSet) error {
 			go retryer.DoAsync(ctx, duty, "fetcher fetch", func(ctx context.Context) error {
 				return clone.FetcherFetch(ctx, duty, set)
 			})
diff --git a/core/scheduler/metrics.go b/core/scheduler/metrics.go
index 1949d88df..23a91e28f 100644
--- a/core/scheduler/metrics.go
+++ b/core/scheduler/metrics.go
@@ -52,8 +52,8 @@ func instrumentSlot(slot slot) {
 }
 
 // instrumentDuty increments the duty counter.
-func instrumentDuty(duty core.Duty, argSet core.FetchArgSet) {
-	for pubkey := range argSet {
+func instrumentDuty(duty core.Duty, defSet core.DutyDefinitionSet) {
+	for pubkey := range defSet {
 		dutyCounter.WithLabelValues(duty.Type.String(), pubkey.String()).Inc()
 	}
 }
diff --git a/core/scheduler/scheduler.go b/core/scheduler/scheduler.go
index f69abe29a..51ad4fef9 100644
--- a/core/scheduler/scheduler.go
+++ b/core/scheduler/scheduler.go
@@ -72,7 +72,7 @@ func New(pubkeys []core.PubKey, eth2Svc eth2client.Service) (*Scheduler, error)
 		eth2Cl:  eth2Cl,
 		pubkeys: pubkeys,
 		quit:    make(chan struct{}),
-		duties:  make(map[core.Duty]core.FetchArgSet),
+		duties:  make(map[core.Duty]core.DutyDefinitionSet),
 		clock:   clockwork.NewRealClock(),
 		delayFunc: func(_ core.Duty, deadline time.Time) <-chan time.Time {
 			return time.After(time.Until(deadline))
@@ -88,14 +88,14 @@ type Scheduler struct {
 	clock         clockwork.Clock
 	delayFunc     delayFunc
 	resolvedEpoch uint64
-	duties        map[core.Duty]core.FetchArgSet
+	duties        map[core.Duty]core.DutyDefinitionSet
 	dutiesMutex   sync.Mutex
-	subs          []func(context.Context, core.Duty, core.FetchArgSet) error
+	subs          []func(context.Context, core.Duty, core.DutyDefinitionSet) error
 }
 
 // Subscribe registers a callback for triggering a duty.
 // Note this should be called *before* Start.
-func (s *Scheduler) Subscribe(fn func(context.Context, core.Duty, core.FetchArgSet) error) {
+func (s *Scheduler) Subscribe(fn func(context.Context, core.Duty, core.DutyDefinitionSet) error) {
 	s.subs = append(s.subs, fn)
 }
 
@@ -132,8 +132,8 @@ func (s *Scheduler) Run() error {
 	}
 }
 
-// GetDuty returns the argSet for a duty if resolved already, otherwise an error.
-func (s *Scheduler) GetDuty(ctx context.Context, duty core.Duty) (core.FetchArgSet, error) {
+// GetDutyDefinition returns the definition for a duty if resolved already, otherwise an error.
+func (s *Scheduler) GetDutyDefinition(ctx context.Context, duty core.Duty) (core.DutyDefinitionSet, error) {
 	slotsPerEpoch, err := s.eth2Cl.SlotsPerEpoch(ctx)
 	if err != nil {
 		return nil, err
@@ -144,12 +144,12 @@ func (s *Scheduler) GetDuty(ctx context.Context, duty core.Duty) (core.FetchArgS
 		return nil, errors.New("epoch not resolved yet")
 	}
 
-	argSet, ok := s.getFetchArgSet(duty)
+	defSet, ok := s.getDutyDefinitionSet(duty)
 	if !ok {
 		return nil, errors.New("duty not resolved although epoch is marked as resolved")
 	}
 
-	return argSet.Clone() // Clone before returning.
+	return defSet.Clone() // Clone before returning.
 }
 
 // scheduleSlot resolves upcoming duties and triggers resolved duties for the slot.
@@ -167,7 +167,7 @@ func (s *Scheduler) scheduleSlot(ctx context.Context, slot slot) {
 			Type: dutyType,
 		}
 
-		argSet, ok := s.getFetchArgSet(duty)
+		defSet, ok := s.getDutyDefinitionSet(duty)
 		if !ok {
 			// Nothing for this duty.
 			continue
@@ -179,13 +179,13 @@ func (s *Scheduler) scheduleSlot(ctx context.Context, slot slot) {
 				return // context cancelled
 			}
 
-			instrumentDuty(duty, argSet)
+			instrumentDuty(duty, defSet)
 			ctx = log.WithCtx(ctx, z.Any("duty", duty))
 			ctx, span := core.StartDutyTrace(ctx, duty, "core/scheduler.scheduleSlot")
 			defer span.End()
 
 			for _, sub := range s.subs {
-				clone, err := argSet.Clone() // Clone for each subscriber.
+				clone, err := defSet.Clone() // Clone for each subscriber.
 				if err != nil {
 					log.Error(ctx, "Cloning duty definition set", err)
 					return
@@ -281,7 +281,7 @@ func (s *Scheduler) resolveAttDuties(ctx context.Context, slot slot, vals valida
 			continue
 		}
 
-		if !s.setFetchArg(duty, pubkey, core.NewAttesterDefinition(attDuty)) {
+		if !s.setDutyDefinition(duty, pubkey, core.NewAttesterDefinition(attDuty)) {
 			continue
 		}
 
@@ -323,7 +323,7 @@ func (s *Scheduler) resolveProDuties(ctx context.Context, slot slot, vals valida
 			continue
 		}
 
-		if !s.setFetchArg(duty, pubkey, core.NewProposerDefinition(proDuty)) {
+		if !s.setDutyDefinition(duty, pubkey, core.NewProposerDefinition(proDuty)) {
 			continue
 		}
 
@@ -337,29 +337,29 @@ func (s *Scheduler) resolveProDuties(ctx context.Context, slot slot, vals valida
 	return nil
 }
 
-func (s *Scheduler) getFetchArgSet(duty core.Duty) (core.FetchArgSet, bool) {
+func (s *Scheduler) getDutyDefinitionSet(duty core.Duty) (core.DutyDefinitionSet, bool) {
 	s.dutiesMutex.Lock()
 	defer s.dutiesMutex.Unlock()
 
-	argSet, ok := s.duties[duty]
+	defSet, ok := s.duties[duty]
 
-	return argSet, ok
+	return defSet, ok
 }
 
-func (s *Scheduler) setFetchArg(duty core.Duty, pubkey core.PubKey, set core.FetchArg) bool {
+func (s *Scheduler) setDutyDefinition(duty core.Duty, pubkey core.PubKey, set core.DutyDefinition) bool {
 	s.dutiesMutex.Lock()
 	defer s.dutiesMutex.Unlock()
 
-	argSet, ok := s.duties[duty]
+	defSet, ok := s.duties[duty]
 	if !ok {
-		argSet = make(core.FetchArgSet)
+		defSet = make(core.DutyDefinitionSet)
 	}
-	if _, ok := argSet[pubkey]; ok {
+	if _, ok := defSet[pubkey]; ok {
 		return false
 	}
 
-	argSet[pubkey] = set
-	s.duties[duty] = argSet
+	defSet[pubkey] = set
+	s.duties[duty] = defSet
 
 	return true
 }
diff --git a/core/scheduler/scheduler_test.go b/core/scheduler/scheduler_test.go
index 1cc78ebd0..e67a29bca 100644
--- a/core/scheduler/scheduler_test.go
+++ b/core/scheduler/scheduler_test.go
@@ -74,7 +74,7 @@ func TestIntegration(t *testing.T) {
 
 	count := 10
 
-	s.Subscribe(func(ctx context.Context, duty core.Duty, set core.FetchArgSet) error {
+	s.Subscribe(func(ctx context.Context, duty core.Duty, set core.DutyDefinitionSet) error {
 		for idx, data := range set {
 			t.Logf("Duty triggered: vidx=%v slot=%v committee=%v\n", idx, duty.Slot, data.(core.AttesterDefinition).CommitteeIndex)
 		}
@@ -242,13 +242,13 @@ func TestSchedulerDuties(t *testing.T) {
 				Time       string
 				DutyStr    string    `json:"duty"`
 				Duty       core.Duty `json:"-"`
-				DutyArgSet map[core.PubKey]string
+				DutyDefSet map[core.PubKey]string
 			}
 			var (
 				results []result
 				mu      sync.Mutex
 			)
-			sched.Subscribe(func(ctx context.Context, duty core.Duty, set core.FetchArgSet) error {
+			sched.Subscribe(func(ctx context.Context, duty core.Duty, set core.DutyDefinitionSet) error {
 				// Make result human-readable
 				resultSet := make(map[core.PubKey]string)
 				for pubkey, def := range set {
@@ -264,7 +264,7 @@ func TestSchedulerDuties(t *testing.T) {
 				results = append(results, result{
 					Duty:       duty,
 					DutyStr:    duty.String(),
-					DutyArgSet: resultSet,
+					DutyDefSet: resultSet,
 				})
 
 				if len(results) == test.Results {
@@ -316,7 +316,7 @@ func TestScheduler_GetDuty(t *testing.T) {
 	clock := newTestClock(t0)
 	sched := scheduler.NewForT(t, clock, new(delayer).delay, pubkeys, eth2Cl)
 
-	_, err = sched.GetDuty(context.Background(), core.Duty{Slot: 0, Type: core.DutyAttester})
+	_, err = sched.GetDutyDefinition(context.Background(), core.Duty{Slot: 0, Type: core.DutyAttester})
 	// due to current design we will return an error if we request the duty of a slot that has not been resolved
 	// by the scheduler yet. With DutyResolver, we will have always an answer
 	require.Error(t, err, "epoch not resolved yet")
@@ -325,7 +325,7 @@ func TestScheduler_GetDuty(t *testing.T) {
 	require.NoError(t, err)
 
 	clock.CallbackAfter(t0.Add(slotDuration).Add(time.Second), func() {
-		res, err := sched.GetDuty(context.Background(), core.Duty{Slot: 0, Type: core.DutyAttester})
+		res, err := sched.GetDutyDefinition(context.Background(), core.Duty{Slot: 0, Type: core.DutyAttester})
 
 		require.NoError(t, err)
 
diff --git a/core/scheduler/testdata/TestSchedulerDuties_grouped.golden b/core/scheduler/testdata/TestSchedulerDuties_grouped.golden
index 30aba5fd2..ed8d13241 100644
--- a/core/scheduler/testdata/TestSchedulerDuties_grouped.golden
+++ b/core/scheduler/testdata/TestSchedulerDuties_grouped.golden
@@ -2,14 +2,14 @@
  {
   "Time": "00:00.000",
   "duty": "0/proposer",
-  "DutyArgSet": {
+  "DutyDefSet": {
    "0x914cff835a769156ba43ad50b931083c2dadd94e8359ce394bc7a3e06424d0214922ddf15f81640530b9c25c0bc0d490": "{\"pubkey\":\"0x914cff835a769156ba43ad50b931083c2dadd94e8359ce394bc7a3e06424d0214922ddf15f81640530b9c25c0bc0d490\",\"slot\":\"0\",\"validator_index\":\"1\"}"
   }
  },
  {
   "Time": "00:04.000",
   "duty": "0/attester",
-  "DutyArgSet": {
+  "DutyDefSet": {
    "0x8dae41352b69f2b3a1c0b05330c1bf65f03730c520273028864b11fcb94d8ce8f26d64f979a0ee3025467f45fd2241ea": "{\"pubkey\":\"0x8dae41352b69f2b3a1c0b05330c1bf65f03730c520273028864b11fcb94d8ce8f26d64f979a0ee3025467f45fd2241ea\",\"slot\":\"0\",\"validator_index\":\"2\",\"committee_index\":\"0\",\"committee_length\":\"16\",\"committees_at_slot\":\"16\",\"validator_committee_index\":\"2\"}",
    "0x8ee91545183c8c2db86633626f5074fd8ef93c4c9b7a2879ad1768f600c5b5906c3af20d47de42c3b032956fa8db1a76": "{\"pubkey\":\"0x8ee91545183c8c2db86633626f5074fd8ef93c4c9b7a2879ad1768f600c5b5906c3af20d47de42c3b032956fa8db1a76\",\"slot\":\"0\",\"validator_index\":\"3\",\"committee_index\":\"0\",\"committee_length\":\"16\",\"committees_at_slot\":\"16\",\"validator_committee_index\":\"3\"}",
    "0x914cff835a769156ba43ad50b931083c2dadd94e8359ce394bc7a3e06424d0214922ddf15f81640530b9c25c0bc0d490": "{\"pubkey\":\"0x914cff835a769156ba43ad50b931083c2dadd94e8359ce394bc7a3e06424d0214922ddf15f81640530b9c25c0bc0d490\",\"slot\":\"0\",\"validator_index\":\"1\",\"committee_index\":\"0\",\"committee_length\":\"16\",\"committees_at_slot\":\"16\",\"validator_committee_index\":\"1\"}"
diff --git a/core/scheduler/testdata/TestSchedulerDuties_spread.golden b/core/scheduler/testdata/TestSchedulerDuties_spread.golden
index e639ebc05..b141bfd2d 100644
--- a/core/scheduler/testdata/TestSchedulerDuties_spread.golden
+++ b/core/scheduler/testdata/TestSchedulerDuties_spread.golden
@@ -2,42 +2,42 @@
  {
   "Time": "00:00.000",
   "duty": "0/proposer",
-  "DutyArgSet": {
+  "DutyDefSet": {
    "0x914cff835a769156ba43ad50b931083c2dadd94e8359ce394bc7a3e06424d0214922ddf15f81640530b9c25c0bc0d490": "{\"pubkey\":\"0x914cff835a769156ba43ad50b931083c2dadd94e8359ce394bc7a3e06424d0214922ddf15f81640530b9c25c0bc0d490\",\"slot\":\"0\",\"validator_index\":\"1\"}"
   }
  },
  {
   "Time": "00:04.000",
   "duty": "0/attester",
-  "DutyArgSet": {
+  "DutyDefSet": {
    "0x914cff835a769156ba43ad50b931083c2dadd94e8359ce394bc7a3e06424d0214922ddf15f81640530b9c25c0bc0d490": "{\"pubkey\":\"0x914cff835a769156ba43ad50b931083c2dadd94e8359ce394bc7a3e06424d0214922ddf15f81640530b9c25c0bc0d490\",\"slot\":\"0\",\"validator_index\":\"1\",\"committee_index\":\"0\",\"committee_length\":\"16\",\"committees_at_slot\":\"16\",\"validator_committee_index\":\"1\"}"
   }
  },
  {
   "Time": "00:00.000",
   "duty": "1/proposer",
-  "DutyArgSet": {
+  "DutyDefSet": {
    "0x8dae41352b69f2b3a1c0b05330c1bf65f03730c520273028864b11fcb94d8ce8f26d64f979a0ee3025467f45fd2241ea": "{\"pubkey\":\"0x8dae41352b69f2b3a1c0b05330c1bf65f03730c520273028864b11fcb94d8ce8f26d64f979a0ee3025467f45fd2241ea\",\"slot\":\"1\",\"validator_index\":\"2\"}"
   }
  },
  {
   "Time": "00:16.000",
   "duty": "1/attester",
-  "DutyArgSet": {
+  "DutyDefSet": {
    "0x8dae41352b69f2b3a1c0b05330c1bf65f03730c520273028864b11fcb94d8ce8f26d64f979a0ee3025467f45fd2241ea": "{\"pubkey\":\"0x8dae41352b69f2b3a1c0b05330c1bf65f03730c520273028864b11fcb94d8ce8f26d64f979a0ee3025467f45fd2241ea\",\"slot\":\"1\",\"validator_index\":\"2\",\"committee_index\":\"1\",\"committee_length\":\"16\",\"committees_at_slot\":\"16\",\"validator_committee_index\":\"2\"}"
   }
  },
  {
   "Time": "00:00.000",
   "duty": "2/proposer",
-  "DutyArgSet": {
+  "DutyDefSet": {
    "0x8ee91545183c8c2db86633626f5074fd8ef93c4c9b7a2879ad1768f600c5b5906c3af20d47de42c3b032956fa8db1a76": "{\"pubkey\":\"0x8ee91545183c8c2db86633626f5074fd8ef93c4c9b7a2879ad1768f600c5b5906c3af20d47de42c3b032956fa8db1a76\",\"slot\":\"2\",\"validator_index\":\"3\"}"
   }
  },
  {
   "Time": "00:28.000",
   "duty": "2/attester",
-  "DutyArgSet": {
+  "DutyDefSet": {
    "0x8ee91545183c8c2db86633626f5074fd8ef93c4c9b7a2879ad1768f600c5b5906c3af20d47de42c3b032956fa8db1a76": "{\"pubkey\":\"0x8ee91545183c8c2db86633626f5074fd8ef93c4c9b7a2879ad1768f600c5b5906c3af20d47de42c3b032956fa8db1a76\",\"slot\":\"2\",\"validator_index\":\"3\",\"committee_index\":\"2\",\"committee_length\":\"16\",\"committees_at_slot\":\"16\",\"validator_committee_index\":\"3\"}"
   }
  }
diff --git a/core/scheduler/testdata/TestSchedulerDuties_spread_errors.golden b/core/scheduler/testdata/TestSchedulerDuties_spread_errors.golden
index 0a84871fc..c5cccbc9e 100644
--- a/core/scheduler/testdata/TestSchedulerDuties_spread_errors.golden
+++ b/core/scheduler/testdata/TestSchedulerDuties_spread_errors.golden
@@ -2,35 +2,35 @@
  {
   "Time": "00:04.000",
   "duty": "0/attester",
-  "DutyArgSet": {
+  "DutyDefSet": {
    "0x914cff835a769156ba43ad50b931083c2dadd94e8359ce394bc7a3e06424d0214922ddf15f81640530b9c25c0bc0d490": "{\"pubkey\":\"0x914cff835a769156ba43ad50b931083c2dadd94e8359ce394bc7a3e06424d0214922ddf15f81640530b9c25c0bc0d490\",\"slot\":\"0\",\"validator_index\":\"1\",\"committee_index\":\"0\",\"committee_length\":\"16\",\"committees_at_slot\":\"16\",\"validator_committee_index\":\"1\"}"
   }
  },
  {
   "Time": "00:00.000",
   "duty": "1/proposer",
-  "DutyArgSet": {
+  "DutyDefSet": {
    "0x8dae41352b69f2b3a1c0b05330c1bf65f03730c520273028864b11fcb94d8ce8f26d64f979a0ee3025467f45fd2241ea": "{\"pubkey\":\"0x8dae41352b69f2b3a1c0b05330c1bf65f03730c520273028864b11fcb94d8ce8f26d64f979a0ee3025467f45fd2241ea\",\"slot\":\"1\",\"validator_index\":\"2\"}"
   }
  },
  {
   "Time": "00:16.000",
   "duty": "1/attester",
-  "DutyArgSet": {
+  "DutyDefSet": {
    "0x8dae41352b69f2b3a1c0b05330c1bf65f03730c520273028864b11fcb94d8ce8f26d64f979a0ee3025467f45fd2241ea": "{\"pubkey\":\"0x8dae41352b69f2b3a1c0b05330c1bf65f03730c520273028864b11fcb94d8ce8f26d64f979a0ee3025467f45fd2241ea\",\"slot\":\"1\",\"validator_index\":\"2\",\"committee_index\":\"1\",\"committee_length\":\"16\",\"committees_at_slot\":\"16\",\"validator_committee_index\":\"2\"}"
   }
  },
  {
   "Time": "00:00.000",
   "duty": "2/proposer",
-  "DutyArgSet": {
+  "DutyDefSet": {
    "0x8ee91545183c8c2db86633626f5074fd8ef93c4c9b7a2879ad1768f600c5b5906c3af20d47de42c3b032956fa8db1a76": "{\"pubkey\":\"0x8ee91545183c8c2db86633626f5074fd8ef93c4c9b7a2879ad1768f600c5b5906c3af20d47de42c3b032956fa8db1a76\",\"slot\":\"2\",\"validator_index\":\"3\"}"
   }
  },
  {
   "Time": "00:28.000",
   "duty": "2/attester",
-  "DutyArgSet": {
+  "DutyDefSet": {
    "0x8ee91545183c8c2db86633626f5074fd8ef93c4c9b7a2879ad1768f600c5b5906c3af20d47de42c3b032956fa8db1a76": "{\"pubkey\":\"0x8ee91545183c8c2db86633626f5074fd8ef93c4c9b7a2879ad1768f600c5b5906c3af20d47de42c3b032956fa8db1a76\",\"slot\":\"2\",\"validator_index\":\"3\",\"committee_index\":\"2\",\"committee_length\":\"16\",\"committees_at_slot\":\"16\",\"validator_committee_index\":\"3\"}"
   }
  }
diff --git a/core/tracing.go b/core/tracing.go
index 1596fd1ec..d8a034a4a 100644
--- a/core/tracing.go
+++ b/core/tracing.go
@@ -66,7 +66,7 @@ func WithTracing() WireOption {
 	return func(w *wireFuncs) {
 		clone := *w
 
-		w.FetcherFetch = func(parent context.Context, duty Duty, set FetchArgSet) error {
+		w.FetcherFetch = func(parent context.Context, duty Duty, set DutyDefinitionSet) error {
 			ctx, span := tracer.Start(parent, "core/fetcher.Fetch")
 			defer span.End()
 
diff --git a/core/types.go b/core/types.go
index b79e27df8..a6c1045f3 100644
--- a/core/types.go
+++ b/core/types.go
@@ -168,26 +168,23 @@ func (k PubKey) ToETH2() (eth2p0.BLSPubKey, error) {
 	return resp, nil
 }
 
-// FetchArg defines a duty containing the parameters required
+// DutyDefinition defines the duty including parameters required
 // to fetch the duty data, it is the result of resolving duties
 // at the start of an epoch.
-// TODO(corver): Rename to DutyDefinition.
-type FetchArg interface {
-	// Clone returns a cloned copy of the FetchArg. For an immutable core workflow architecture,
-	// remember to clone data when it leaves the current scope (sharing, storing, returning, etc).
-	Clone() (FetchArg, error)
-	// Marshaler returns the json serialised unsigned duty data.
+type DutyDefinition interface {
+	// Clone returns a cloned copy of the DutyDefinition.
+	Clone() (DutyDefinition, error)
+	// Marshaler returns the json serialised duty definition.
 	json.Marshaler
 }
 
-// FetchArgSet is a set of fetch args, one per validator.
-// TODO(corver): Rename to DutyDefinitionSet.
-type FetchArgSet map[PubKey]FetchArg
+// DutyDefinitionSet is a set of duty definitions, one per validator.
+type DutyDefinitionSet map[PubKey]DutyDefinition
 
-// Clone returns a cloned copy of the FetchArgSet. For an immutable core workflow architecture,
+// Clone returns a cloned copy of the DutyDefinitionSet. For an immutable core workflow architecture,
 // remember to clone data when it leaves the current scope (sharing, storing, returning, etc).
-func (s FetchArgSet) Clone() (FetchArgSet, error) {
-	resp := make(FetchArgSet, len(s))
+func (s DutyDefinitionSet) Clone() (DutyDefinitionSet, error) {
+	resp := make(DutyDefinitionSet, len(s))
 	for key, data := range s {
 		var err error
 		resp[key], err = data.Clone()
diff --git a/core/validatorapi/validatorapi.go b/core/validatorapi/validatorapi.go
index bfda9531e..b88454700 100644
--- a/core/validatorapi/validatorapi.go
+++ b/core/validatorapi/validatorapi.go
@@ -156,7 +156,7 @@ type Component struct {
 	pubKeyByAttFunc func(ctx context.Context, slot, commIdx, valCommIdx int64) (core.PubKey, error)
 	awaitAttFunc    func(ctx context.Context, slot, commIdx int64) (*eth2p0.AttestationData, error)
 	awaitBlockFunc  func(ctx context.Context, slot int64) (*spec.VersionedBeaconBlock, error)
-	getDutyFunc     func(ctx context.Context, duty core.Duty) (core.FetchArgSet, error)
+	dutyDefFunc     func(ctx context.Context, duty core.Duty) (core.DutyDefinitionSet, error)
 	parSigDBFuncs   []func(context.Context, core.Duty, core.ParSignedDataSet) error
 }
 
@@ -191,10 +191,10 @@ func (c *Component) RegisterPubKeyByAttestation(fn func(ctx context.Context, slo
 	c.pubKeyByAttFunc = fn
 }
 
-// RegisterGetDutyFunc registers a function to query duty data by duty.
+// RegisterDutyDefinitionFunc registers a function to query duty definitions.
 // It supports a single function, since it is an input of the component.
-func (c *Component) RegisterGetDutyFunc(fn func(ctx context.Context, duty core.Duty) (core.FetchArgSet, error)) {
-	c.getDutyFunc = fn
+func (c *Component) RegisterGetDutyDefinition(fn func(ctx context.Context, duty core.Duty) (core.DutyDefinitionSet, error)) {
+	c.dutyDefFunc = fn
 }
 
 // RegisterParSigDB registers a partial signed data set store function.
@@ -635,16 +635,16 @@ func (c Component) epochFromSlot(ctx context.Context, slot eth2p0.Slot) (eth2p0.
 
 func (c Component) getProposerPubkey(ctx context.Context, slot eth2p0.Slot) (core.PubKey, error) {
 	// Get proposer pubkey (this is a blocking query).
-	dutySet, err := c.getDutyFunc(ctx, core.Duty{Slot: int64(slot), Type: core.DutyProposer})
+	defSet, err := c.dutyDefFunc(ctx, core.NewProposerDuty(int64(slot)))
 	if err != nil {
 		return "", err
-	} else if len(dutySet) != 1 {
+	} else if len(defSet) != 1 {
 		return "", errors.New("unexpected amount of proposer duties")
 	}
 
 	// There should be single duty proposer for the slot
 	var pubkey core.PubKey
-	for pk := range dutySet {
+	for pk := range defSet {
 		pubkey = pk
 	}
 
diff --git a/core/validatorapi/validatorapi_test.go b/core/validatorapi/validatorapi_test.go
index b1d87e8d7..98f7bb1f3 100644
--- a/core/validatorapi/validatorapi_test.go
+++ b/core/validatorapi/validatorapi_test.go
@@ -351,8 +351,8 @@ func TestComponent_BeaconBlockProposal(t *testing.T) {
 	block1.Phase0.ProposerIndex = vIdx
 	block1.Phase0.Body.RANDAOReveal = randao
 
-	component.RegisterGetDutyFunc(func(ctx context.Context, duty core.Duty) (core.FetchArgSet, error) {
-		return core.FetchArgSet{pubkey: nil}, nil
+	component.RegisterGetDutyDefinition(func(ctx context.Context, duty core.Duty) (core.DutyDefinitionSet, error) {
+		return core.DutyDefinitionSet{pubkey: nil}, nil
 	})
 
 	component.RegisterAwaitBeaconBlock(func(ctx context.Context, slot int64) (*spec.VersionedBeaconBlock, error) {
@@ -413,8 +413,8 @@ func TestComponent_SubmitBeaconBlock(t *testing.T) {
 	unsignedBlock.Phase0.Slot = slot
 	unsignedBlock.Phase0.ProposerIndex = vIdx
 
-	vapi.RegisterGetDutyFunc(func(ctx context.Context, duty core.Duty) (core.FetchArgSet, error) {
-		return core.FetchArgSet{corePubKey: nil}, nil
+	vapi.RegisterGetDutyDefinition(func(ctx context.Context, duty core.Duty) (core.DutyDefinitionSet, error) {
+		return core.DutyDefinitionSet{corePubKey: nil}, nil
 	})
 
 	// Sign beacon block
@@ -491,8 +491,8 @@ func TestComponent_SubmitBeaconBlockInvalidSignature(t *testing.T) {
 	unsignedBlock.Phase0.Slot = slot
 	unsignedBlock.Phase0.ProposerIndex = vIdx
 
-	vapi.RegisterGetDutyFunc(func(ctx context.Context, duty core.Duty) (core.FetchArgSet, error) {
-		return core.FetchArgSet{corePubKey: nil}, nil
+	vapi.RegisterGetDutyDefinition(func(ctx context.Context, duty core.Duty) (core.DutyDefinitionSet, error) {
+		return core.DutyDefinitionSet{corePubKey: nil}, nil
 	})
 
 	// Add invalid Signature to beacon block
@@ -541,8 +541,8 @@ func TestComponent_SubmitBeaconBlockInvalidBlock(t *testing.T) {
 	vapi, err := validatorapi.NewComponent(bmock, pubShareByKey, 0)
 	require.NoError(t, err)
 
-	vapi.RegisterGetDutyFunc(func(ctx context.Context, duty core.Duty) (core.FetchArgSet, error) {
-		return core.FetchArgSet{pubkey: nil}, nil
+	vapi.RegisterGetDutyDefinition(func(ctx context.Context, duty core.Duty) (core.DutyDefinitionSet, error) {
+		return core.DutyDefinitionSet{pubkey: nil}, nil
 	})
 
 	// invalid block scenarios
diff --git a/docs/architecture.md b/docs/architecture.md
index 8d33e4abe..94ec377b7 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -117,7 +117,7 @@ We define the following duty types:
 - `DutyProposer = 1`: Proposing a block
 - `DutyAttester = 2`: Creating an attestation
 - `DutyRandao = 3`: Creating a randao reveal signature required as input to DutyProposer
-- `DutyAggregator = 4`: Aggregating attestations
+- `DutyExit = 4`: Voluntary exit
 
 > ℹ️ Duty is on a cluster level, not a DV level. A duty defines the “unit of work” for the whole cluster,
 > not just a single DV. This allows the workflow to aggregate and batch multiple DVs in some steps, specifically consensus.
@@ -145,20 +145,38 @@ and [Get block proposer](https://ethereum.github.io/beacon-APIs/#/ValidatorRequi
 at the end of each epoch for the next epoch. It then caches the results returned and triggers the duty
 when the associated slot starts.
 
-An abstract `FetchArg` type is defined that represents the json formatted responses returned by the beacon node above.
+An abstract `DutyDefinition` type is defined that represents the json formatted responses returned by the beacon node above.
+Note the ETH2 spec refers to these as "duties", but we use a slightly different term to avoid overloading
+the term "duty" which we defined above.
 ```go
-// FetchArg contains the arguments required to fetch the duty data,
-// it is the result of resolving duties at the start of an epoch.
-type FetchArg []byte
+// DutyDefinition defines a duty including parameters required
+// to fetch the duty data, it is the result of resolving duties
+// at the start of an epoch.
+type DutyDefinition interface {
+  // Clone returns a cloned copy of the DutyDefinition.
+  Clone() (DutyDefinition, error)
+  // Marshaler returns the json serialised duty definition.
+  json.Marshaler
+}
 ```
+
+The following `DutyDefinition` implementations are provided:
+ - `AttesterDefinition` which wraps "Get attester duties" response above.
+ - `ProposerDefinition` which wraps "Get block proposer" response above.
+
 Since a cluster can contain multiple DVs, it may have to perform multiple similar duties for the same slot, e.g. `DutyAttester`.
-Multiple `FetchArg`s are combined into a single `FetchArgSet` that is defined as:
+Multiple `DutyDefinition`s are combined into a single `DutyDefinitionSet` that is defined as:
 ```go
-// FetchArgSet is a set of fetch args, one per validator.
-type FetchArgSet map[PubKey]FetchArg
+// DutyDefinitionSet is a set of fetch args, one per validator.
+type DutyDefinitionSet map[PubKey]DutyDefinition
 ```
 
-Note the `DutyRandao` isn’t scheduled by the scheduler, since it is initiated directly by VC at the start of the epoch.
+Note the `DutyRandao` and `DutyExit` isn’t scheduled by the scheduler, since they are initiated directly by VC.
+
+> ℹ️ The core workflow follows the immutable architecture approach, with immutable self-contained values flowing between components.
+> Values can be thought of as events or messages and components can be thought of as actors consuming and generating events.
+> This however requires that values are immutable. All abstract value types therefore define a `Clone` method
+> that must be called before a value leaves its scope (shared, cached, returned etc.).
 
 > 🏗️ TODO: Define the exact timing requirements for different duties.
 
@@ -167,10 +185,10 @@ The scheduler interface is defined as:
 // Scheduler triggers the start of a duty workflow.
 type Scheduler interface {
   // Subscribe registers a callback for triggering a duty.
-  Subscribe(func(context.Context, Duty, FetchArgSet) error)
+  Subscribe(func(context.Context, Duty, DutyDefinitionSet) error)
 
-  // GetDuty returns the argSet for a duty if resolved already.
-  GetDuty(context.Context, Duty) (FetchArgSet, error)
+  // GetDutyDefinition returns the definition for a duty if already resolved.
+  GetDutyDefinition(context.Context, Duty) (DutyDefinitionSet, error)
 }
 ```
 > ℹ️ Components of the workflow are decoupled from each other. They are stitched together by callback subscriptions.
@@ -186,14 +204,18 @@ For `DutyProposer` it fetches a previously aggregated randao_reveal from the `Ag
 from the beacon node.
 
 An abstract `UnsignedData` type is defined to represent either `AttestationData` or `BeaconBlock` depending on the `DutyType`.
-It contains the standard serialised json format of the data as returned from beacon node.
 
 ```go
 // UnsignedData represents an unsigned duty data object.
-type UnsignedData []byte
+type UnsignedData interface {
+  // Clone returns a cloned copy of the UnsignedData.
+  Clone() (UnsignedData, error)
+  // Marshaler returns the json serialised unsigned duty data.
+  json.Marshaler
+}
 ```
 
-Since the input to fetcher is a `FetchArgSet`, it fetches multiple `UnsignedData` objects for the same `Duty`.
+Since the input to fetcher is a `DutyDefinitionSet`, it fetches multiple `UnsignedData` objects for the same `Duty`.
 Multiple `UnsignedData`s are combined into a single `UnsignedDataSet` that is defined as:
 ```go
 // UnsignedDataSet is a set of unsigned duty data objects, one per validator.
@@ -212,7 +234,7 @@ The fetcher interface is defined as:
 // Fetcher fetches proposed duty data.
 type Fetcher interface {
   // Fetch triggers fetching of a proposed duty data set.
-  Fetch(context.Context, Duty, FetchArgSet) error
+  Fetch(context.Context, Duty, DutyDefinitionSet) error
 
   // Subscribe registers a callback for proposed duty data sets.
   Subscribe(func(context.Context, Duty, UnsignedDataSet) error)
@@ -315,19 +337,32 @@ The validator API provides a [beacon-node API](https://ethereum.github.io/beacon
 intercepting some calls and proxying others directly to the upstream beacon node.
 It mostly serves unsigned duty data requests from the `DutyDB` and sends the resulting partial signed duty objects to the `ParSigDB`.
 
-Partial signed duty data objects are defined as `ParSignedData`:
+Partial signed duty data values are defined as `ParSignedData` which extend `SignedData` values:
 ```go
-// ParSignedData is a partially signed duty data.
-// Partial refers to it being signed by a single share of the BLS threshold signing scheme.
+// SignedData is a signed duty data.
+type SignedData interface {
+  // Signature returns the signed duty data's signature.
+  Signature() Signature
+  // SetSignature returns a copy of signed duty data with the signature replaced.
+  SetSignature(Signature) (SignedData, error)
+  // Clone returns a cloned copy of the SignedData.
+  Clone() (SignedData, error)
+  // Marshaler returns the json serialised signed duty data (including the signature).
+  json.Marshaler
+}
+
+// ParSignedData is a partially signed duty data only signed by a single threshold BLS share.
 type ParSignedData struct {
-  // Data is the partially signed duty data received from VC.
-  Data []byte
-  // Signature of tbls share extracted from data.
-  Signature []byte
-  // Index of the tbls share.
-  Index int
+  // SignedData is a partially signed duty data.
+  SignedData
+  // ShareIdx returns the threshold BLS share index.
+  ShareIdx int
 }
+
 ```
+
+The following `SignedData` implementations are provided: `Attestation`, `VersionedSignedBeaconBlock`, `SignedVoluntaryExit`, and `Signature` which is just a signature without any data used for `DutyRandao`.
+
 Multiple `ParSignedData` are combined into a single `ParSignedDataSet` defines as follows:
 ```go
 // ParSignedDataSet is a set of partially signed duty data objects, one per validator.
@@ -370,7 +405,7 @@ the public share (what the VC thinks as its public key) to and from the DV root
 > 🏗️ TODO: Figure out other endpoints required.
 
 The validator api interface is defined as:
-```
+```go
 // ValidatorAPI provides a beacon node API to validator clients. It serves duty data from the
 // DutyDB and stores partial signed data in the ParSigDB.
 type ValidatorAPI interface {
@@ -378,7 +413,7 @@ type ValidatorAPI interface {
 	RegisterAwaitBeaconBlock(func(context.Context, slot int) (beaconapi.BeaconBlock, error))
 
 	// RegisterGetDutyFunc registers a function to query duty data.
-	RegisterGetDutyFunc(func(ctx context.Context, duty Duty) (FetchArgSet, error))
+	RegisterGetDutyFunc(func(ctx context.Context, duty Duty) (DutyDefinitionSet, error))
 
 	// RegisterAwaitAttestation registers a function to query attestation data.
 	RegisterAwaitAttestation(func(context.Context, slot int, commIdx int) (*beaconapi.AttestationData, error))
@@ -401,7 +436,7 @@ Duties originating in the `scheduler` (`DutyAttester`, `DutyProposer`) are not s
 Instead of waiting for the `validatorapi` to submit signatures, these duties directly request
 signatures from the remote signer instance. The flow is otherwise unaffected.
 
-Duties originating in the `validatorapi` (`DutyRandao`, `DutyAggregator`) has to refactored to
+Duties originating in the `validatorapi` (`DutyRandao`, `DutyExit`) has to refactored to
 originate in the `scheduler`, since charon is in full control of the duties in this architecture.
 
 The overall core workflow remains the same, `scheduler` just schedules all the duties.
@@ -508,17 +543,7 @@ type ParSigEx interface {
 The signature aggregation service aggregates partial BLS signatures and sends them to the `bcast` component and persists them to the `AggSigDB`.
 It is a stateless pure function.
 
-Aggregated signed duty data objects are defined as `SignedData`:
-```go
-// SignedData is an aggregated signed duty data.
-// Aggregated refers to it being signed by the aggregated BLS threshold signing scheme.
-type SignedData struct {
-  // Data is the signed duty data to be sent to beacon chain.
-  Data []byte
-  // Signature is the result of tbls aggregation and is inserted into the data.
-  Signature []byte
-}
-```
+Aggregated signed duty data objects are defined as `SignedData` defined above.
 
 The signature aggregation interface is defined as:
 ```go
diff --git a/docs/structure.md b/docs/structure.md
index 3378e8b6b..ea8939876 100644
--- a/docs/structure.md
+++ b/docs/structure.md
@@ -27,7 +27,7 @@ charon/             # project root
 │
 ├─ core/            # core workflow; charon business logic (see architecture doc for details)
 │  ├─ interfaces.go # component interfaces: Scheduler, Fetcher, Consensus, etc.
-│  ├─ types.go      # core workflow types: Duty, PubKey, FetchArg, UnsignedData, etc.
+│  ├─ types.go      # core workflow types: Duty, PubKey, DutyDefinition, UnsignedData, etc.
 │  ├─ encode.go     # encode/decode the abstract types with type safe API
 │  │
 │  │                # core workflow component implementations