diff --git a/error/chain-error.go b/error/chain-error.go
index d427330..e084ced 100644
--- a/error/chain-error.go
+++ b/error/chain-error.go
@@ -3,41 +3,33 @@
 package error
 
 import (
-	"memar/protocol"
+	error_p "memar/error/protocol"
 )
 
+// PastChain unwrap an error and return last chain of error.
+func PastChain(err error_p.Error) (last error_p.Error) {
+	var chainedError, ok = err.(error_p.Chain)
+	if ok {
+		return chainedError.PastChain()
+	}
+	return
+}
+
 // NewChain wrap an error and additional information usually use in logging to save more details about error.
-func NewChain(err *Error, info string) (ce *ChainError) {
-	if err == nil {
+func NewChain(err error_p.Error, chain error_p.Error) (ce *ChainError) {
+	if err == nil || chain == nil {
 		return
 	}
 	return &ChainError{
-		Err:  err,
-		info: info,
+		Error: err,
+		chain: chain,
 	}
 }
 
 // ChainError is a extended implementation of Error to carry custom details along error.
 type ChainError struct {
-	*Err
-	info string
-}
-
-func (ce *ChainError) PastChain() protocol.Error { return ce.Err }
-
-//memar:impl memar/protocol.Stringer
-func (ce *ChainError) ToString() string {
-	return "\n" + ce.Err.ToString() + "\n	Chain Info: " + ce.info
+	error_p.Error
+	chain error_p.Error
 }
-func (ce *ChainError) FromString(s string) (err protocol.Error) {
-	// TODO:::
-	return
-}
-
-// Go compatibility methods. Unwrap provides compatibility for Go 1.13 error chains.
-func (ce *ChainError) Error() string { return ce.ToString() }
-func (ce *ChainError) Cause() error  { return ce.Err }
-func (ce *ChainError) Unwrap() error { return ce.Err }
 
-// func (ce *ChainError) Is(error) bool
-// func (ce *ChainError) As(any) bool
+func (ce *ChainError) PastChain() error_p.Error { return ce.chain }
diff --git a/error/error-type.go b/error/error-type.go
index bc1ecea..0aab60b 100644
--- a/error/error-type.go
+++ b/error/error-type.go
@@ -3,21 +3,23 @@
 package error
 
 import (
-	"memar/protocol"
+	error_p "memar/error/protocol"
 )
 
-type ErrorType protocol.ErrorType
-
-func (et *ErrorType) Set(errorType protocol.ErrorType)   { *et |= ErrorType(errorType) }
-func (et *ErrorType) Unset(errorType protocol.ErrorType) { *et &= ^ErrorType(errorType) }
-func (et ErrorType) Check(errorType protocol.ErrorType) bool {
-	return errorType&protocol.ErrorType(et) == errorType
+//memar:impl memar/error/protocol.Internal
+func IsInternal(err error_p.Error) bool {
+	var interErr, ok = err.(error_p.Internal)
+	return ok && interErr.Internal()
 }
 
-func (et Error) Internal() bool  { return et.Check(protocol.ErrorType_Internal) }
-func (et Error) Temporary() bool { return et.Check(protocol.ErrorType_Temporary) }
-func (et Error) Timeout() bool   { return et.Check(protocol.ErrorType_Timeout) }
+//memar:impl memar/error/protocol.Temporary
+func IsTemporary(err error_p.Error) bool {
+	var tempErr, ok = err.(error_p.Temporary)
+	return ok && tempErr.Temporary()
+}
 
-func (et *Error) SetInternal()  { et.Set(protocol.ErrorType_Internal) }
-func (et *Error) SetTemporary() { et.Set(protocol.ErrorType_Temporary) }
-func (et *Error) SetTimeout()   { et.Set(protocol.ErrorType_Timeout) }
+//memar:impl memar/error/protocol.Timeout
+func IsTimeout(err error_p.Error) bool {
+	var timeErr, ok = err.(error_p.Timeout)
+	return ok && timeErr.Timeout()
+}
diff --git a/error/error.go b/error/error.go
index 5e0f635..1eb2334 100644
--- a/error/error.go
+++ b/error/error.go
@@ -3,58 +3,20 @@
 package error
 
 import (
-	"memar/datatype"
-	"memar/mediatype"
-	"memar/protocol"
+	error_p "memar/error/protocol"
 )
 
-// Err is the same as the Error.
-// Use this type when embed in other struct to solve field & method same name problem(Error struct and Error() method) to satisfy interfaces.
-type Err = Error
-
-// Error implements protocol.Error
-type Error struct {
-	ErrorType
-
-	mediatype.MT
-	datatype.DataType
-}
-
-// Init initialize Error that implement protocol.Error
-// Never change MediaType due to it adds unnecessary complicated troubleshooting errors on SDK.
-//
-//memar:impl memar/protocol.ObjectLifeCycle
-func (e *Error) Init(mediatype string) (err protocol.Error) {
-	err = e.MT.Init(mediatype)
-	// if err != nil {
-	// 	return
-	// }
-	return
-}
-
-// Equal compare two Error.
-func (e *Error) Equal(err protocol.Error) bool {
-	if e == nil && err == nil {
+// IsEqual compare two Error.
+// Suggest to add more logic to Error.Equal() logic such as chain situation!
+func IsEqual(base, with error_p.Error) bool {
+	if base == nil && with == nil {
 		return true
 	}
-	if e != nil && err != nil && e.ID() == err.ID() {
+	if base != nil &&
+		with != nil &&
+		base.MediaType() == with.MediaType() &&
+		base.DataTypeID() == with.DataTypeID() {
 		return true
 	}
-	// TODO::: check err as chain error
 	return false
 }
-
-func (e *Error) Type() protocol.ErrorType             { return protocol.ErrorType(e.ErrorType) }
-func (e *Error) CheckType(et protocol.ErrorType) bool { return e.ErrorType.Check(et) }
-
-func (e *Error) Notify() {
-	// TODO:::
-}
-
-// Go compatibility methods. Unwrap provides compatibility for Go 1.13 error chains.
-func (e *Error) Error() string { return e.MT.MediaType() }
-func (e *Error) Cause() error  { return nil }
-func (e *Error) Unwrap() error { return nil }
-
-// func (e *Error) Is(error) bool
-// func (e *Error) As(any) bool
diff --git a/error/protocol/error.go b/error/protocol/error.go
index d1d0642..0363667 100644
--- a/error/protocol/error.go
+++ b/error/protocol/error.go
@@ -5,21 +5,24 @@ package error_p
 import (
 	// primitive_p "memar/computer/language/primitive/protocol"
 	datatype_p "memar/datatype/protocol"
+	mediatype_p "memar/mediatype/protocol"
 )
 
 // Error is base behaviors that any Error capsule must implement.
 //
-// It is similar to opaque error model describe here: https://dave.cheney.net/paste/gocon-spring-2016.pdf
-// or this RFC: https://tools.ietf.org/html/rfc7807
+// Other suggestions:
+// - opaque error model: https://dave.cheney.net/paste/gocon-spring-2016.pdf
+// - RFC7807: https://tools.ietf.org/html/rfc7807
+// - https://doc.rust-lang.org/stable/std/error/trait.Error.html
 type Error interface {
 	datatype_p.DataType
+	mediatype_p.MediaType
 
-	// Can't un-comment below due to Golang import cycle problem, So add it manually!
+	// Can't un-comment below due to Golang import cycle problem, So add it manually.
 	// primitive_p.Equivalence[Error]
 	Equal(with Error) bool
 
 	// ADT
-	// MediaType
 
 	// Below methods comment in favor of log_p.Event_Message interface.
 	// Error() string
diff --git a/error/protocol/gui.go b/error/protocol/gui.go
index fc75fdd..b191534 100644
--- a/error/protocol/gui.go
+++ b/error/protocol/gui.go
@@ -2,6 +2,10 @@
 
 package error_p
 
+// GUI indicate how Error capsule must act in GUI applications.
+//
+// GUI can use also in CLI apps by e.g. use `//go:build gui` tag,
+// But strongly suggest DON'T think in this way and just use `Log` concept
 type GUI interface {
 	// Notify error to user by graphic, sound and vibration (Haptic Feedback)
 	Notify()
diff --git a/error/protocol/optional.go b/error/protocol/optional.go
index c0ff022..db75e1b 100644
--- a/error/protocol/optional.go
+++ b/error/protocol/optional.go
@@ -5,6 +5,14 @@ package error_p
 // Belows are some other error behaviors that Errors capsule CAN implement,
 // but any error package can introduce new behaviors for any purpose.
 
+// Chian errors can use in situation that error occurred but can't handle in that layer and
+// Upper layer also can't handle it directly and decide to log it!
+// Use chain errors to return multiple error to caller and
+// Usually caller log them and return another error to caller that almost always SDK client e.g. GUI, Apps, ...
+type Chain interface {
+	PastChain() (last Error)
+}
+
 type Internal interface {
 	// Who cause the error?
 	// Internal	: means calling process logic has runtime bugs like HTTP server error status codes ( 500 – 599 ).
diff --git a/error/util.go b/error/util.go
index dde8334..800557e 100644
--- a/error/util.go
+++ b/error/util.go
@@ -3,20 +3,17 @@
 package error
 
 import (
-	"memar/protocol"
+	error_p "memar/error/protocol"
 )
 
-func ToGoError(err protocol.Error) error {
+func ToGoError(err error_p.Error) error {
 	if err == nil {
 		return nil
 	}
 
-	var exErr = err.(*Error)
-	if exErr != nil {
-		return exErr
-	}
-
-	return &errorString{msg: err.ToString()}
+	var errStr errorString
+	errStr.msg = err.Summary()
+	return &errStr
 }
 
 // errorString is a trivial implementation of error.
@@ -26,15 +23,16 @@ type errorString struct {
 
 func (e *errorString) Error() string { return e.msg }
 
-func ToError(err error) protocol.Error {
+func ToError(err error) error_p.Error {
 	if err == nil {
 		return nil
 	}
 
-	var exErr = err.(*Error)
+	var exErr = err.(error_p.Error)
 	if exErr != nil {
 		return exErr
 	}
+
 	// TODO:::
 	return nil
 }