diff --git a/NAMESPACE b/NAMESPACE
index 1d1541df..bac329c8 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -28,6 +28,7 @@ export(GMLEllipsoidalCS)
 export(GMLGeodeticCRS)
 export(GMLLinearCS)
 export(GMLObliqueCartesianCS)
+export(GMLOperationMethod)
 export(GMLOperationParameter)
 export(GMLOperationParameterGroup)
 export(GMLPolarCS)
diff --git a/R/GMLAbstractGeneralOperationParameter.R b/R/GMLAbstractGeneralOperationParameter.R
new file mode 100644
index 00000000..c94b7bc1
--- /dev/null
+++ b/R/GMLAbstractGeneralOperationParameter.R
@@ -0,0 +1,55 @@
+#' GMLAbstractGeneralOperationParameter
+#'
+#' @docType class
+#' @importFrom R6 R6Class
+#' @export
+#' @keywords ISO GML abstract general operation parameter
+#' @return Object of \code{\link{R6Class}} for modelling an GMLAbstractGeneralOperationParameter
+#' @format \code{\link{R6Class}} object.
+#'
+#' @field minimumOccurs
+#'
+#' @section Inherited methods from \code{GMLDefinition}
+#'
+#' @section Methods:
+#' \describe{
+#'  \item{\code{new(xml, defaults, id)}}{
+#'    This method is used to instantiate a GML AbstractGeneralOperationParameter
+#'  }
+#'  \item{\code{setMinimumOccurs(minimumOccurs)}}{
+#'    Sets the minimum occurs, object of class \code{integer}
+#'  }
+#' }
+#' 
+#' @references 
+#'   ISO 19136:2007 Geographic Information -- Geographic Markup Language.
+#'   http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=32554 
+#'   
+#'   OGC Geography Markup Language. http://www.opengeospatial.org/standards/gml
+#' 
+#' @author Emmanuel Blondel <emmanuel.blondel1@@gmail.com>
+#'
+GMLAbstractGeneralOperationParameter <- R6Class("GMLAbstractGeneralOperationParameter",
+   inherit = GMLDefinition,
+   private = list(
+     xmlElement = "AbstractGeneralOperationParameter",
+     xmlNamespacePrefix = "GML"
+   ),
+   public = list(
+     
+     #+ minimumOccurs [0..1]: integer
+     minimumOccurs = NULL,
+     
+     #setMinimumOccurs
+     setMinimumOccurs = function(minimumOccurs){
+       if(!is(minimumOccurs, "integer")){
+         minimumOccurs <- as.integer(minimumOccurs)
+         if(is.na(minimumOccurs)){
+          stop("The argument value should be an object of class 'integer'")
+         }
+       }
+       self$minimumOccurs <- GMLElement$create("minimumOccurs", value = minimumOccurs)
+     }
+     
+   )
+)
\ No newline at end of file
diff --git a/R/GMLOperationMethod.R b/R/GMLOperationMethod.R
new file mode 100644
index 00000000..60914842
--- /dev/null
+++ b/R/GMLOperationMethod.R
@@ -0,0 +1,112 @@
+#' GMLOperationMethod
+#'
+#' @docType class
+#' @importFrom R6 R6Class
+#' @export
+#' @keywords ISO GML operation method
+#' @return Object of \code{\link{R6Class}} for modelling an GMLOperationMethod
+#' @format \code{\link{R6Class}} object.
+#'
+#' @field formulaCitation
+#' @field sourceDimensions
+#' @field targetDimensions
+#'
+#' @section Inherited methods from \code{GMLDefinition}
+#'
+#' @section Methods:
+#' \describe{
+#'  \item{\code{new(xml, defaults, id)}}{
+#'    This method is used to instantiate a GML OperationMethod
+#'  }
+#'  \item{\code{setFormulaCitation(citation)}}{
+#'    Sets the formula citation, object of class \code{ISOCitation}
+#'  }
+#'  \item{\code{setSourceDimensions(value)}}{
+#'    Sets the number of source dimensions, object of class \code{integer}
+#'  }
+#'  \item{\code{setTargetDimensions(value)}}{
+#'    Sets the number of target dimensions, object of class \code{integer}
+#'  }
+#'  \item{\code{addParameter(parameter)}}{
+#'    Adds a parameter or parameter group, object of class \code{GMLOperationParameter}
+#'    or \code{GMLOperationParameterGroup}
+#'  }
+#'  \item{\code{delParameter(parameter)}}{
+#'    Deletes a parameter or parameter group, object of class \code{GMLOperationParameter}
+#'    or \code{GMLOperationParameterGroupo}
+#'  }
+#' }
+#' 
+#' @references 
+#'   ISO 19136:2007 Geographic Information -- Geographic Markup Language.
+#'   http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=32554 
+#'   
+#'   OGC Geography Markup Language. http://www.opengeospatial.org/standards/gml
+#' 
+#' @author Emmanuel Blondel <emmanuel.blondel1@@gmail.com>
+#'
+GMLOperationMethod <- R6Class("GMLOperationMethod",
+  inherit = GMLDefinition,
+  private = list(
+    xmlElement = "OperationMethod",
+    xmlNamespacePrefix = "GML"
+  ),
+  public = list(
+   
+    #+ formulaCitation [1..1]: ISOCitation
+    formulaCitation = NA,
+    #+ sourceDimensions [0..1]: integer
+    sourceDimensions = NULL,
+    #+ targetDimensions [0..1]: integer
+    targetDimensions = NULL,
+    #+ parameter  [0..*]: GMLOperationParameter or GMLOperationParameterGroup
+    parameter = list(),
+    
+    #setFormulaCitation
+    setFormulaCitation = function(citation){
+      if(!is(citation, "ISOCitation")){
+        stop("The argument value should be an object of class 'ISOCitation'")
+      }
+      self$formulaCitation <- GMLElement$create("formulaCitation", value = citation)
+    },
+    
+    #setSourceDimensions
+    setSourceDimensions = function(value){
+      if(!is(value, "integer")){
+        value <- as.integer(value)
+        if(is.na(value)){
+          stop("The argument value should an object of class or coerceable to 'integer'")
+        }
+      }
+      self$sourceDimensions <- GMLElement$create("sourceDimensions", value = value)
+    },
+    
+    #setTargetDimensions
+    setTargetDimensions = function(value){
+      if(!is(value, "integer")){
+        value <- as.integer(value)
+        if(is.na(value)){
+          stop("The argument value should an object of class or coerceable to 'integer'")
+        }
+      }
+      self$targetDimensions <- GMLElement$create("targetDimensions", value = value)
+    },
+    
+    #addParameter
+    addParameter = function(param){
+      if(!inherits(param, "GMLAbstractGeneralOperationParameter")){
+        stop("The argument value should be an object of class 'GMLOperationParameter' or 'GMLOperationParameterGroup'")
+      }
+      return(self$addListElement("parameter", GMLElement$create("parameter", value = param)))
+    },
+    
+    #delParameter
+    delParameter = function(param){
+      if(!inherits(param, "GMLAbstractGeneralOperationParameter")){
+        stop("The argument value should be an object of class 'GMLOperationParameter' or 'GMLOperationParameterGroup'")
+      }
+      return(self$delListElement("parameter", GMLElement$create("parameter", value = param)))
+    }
+    
+  )
+)
\ No newline at end of file
diff --git a/R/GMLOperationParameter.R b/R/GMLOperationParameter.R
new file mode 100644
index 00000000..87658201
--- /dev/null
+++ b/R/GMLOperationParameter.R
@@ -0,0 +1,34 @@
+#' GMLOperationParameter
+#'
+#' @docType class
+#' @importFrom R6 R6Class
+#' @export
+#' @keywords ISO GML operation parameter
+#' @return Object of \code{\link{R6Class}} for modelling an GMLOperationParameter
+#' @format \code{\link{R6Class}} object.
+#'
+#' @section Inherited methods from \code{GMLAbstractGeneralOperationParameter}
+#'
+#' @section Methods:
+#' \describe{
+#'  \item{\code{new(xml, defaults, id)}}{
+#'    This method is used to instantiate a GML OperationParameter
+#'  }
+#' }
+#' 
+#' @references 
+#'   ISO 19136:2007 Geographic Information -- Geographic Markup Language.
+#'   http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=32554 
+#'   
+#'   OGC Geography Markup Language. http://www.opengeospatial.org/standards/gml
+#' 
+#' @author Emmanuel Blondel <emmanuel.blondel1@@gmail.com>
+#'
+GMLOperationParameter <- R6Class("GMLOperationParameter",
+  inherit = GMLAbstractGeneralOperationParameter,
+  private = list(
+    xmlElement = "OperationParameter",
+    xmlNamespacePrefix = "GML"
+  ),
+  public = list()
+)
\ No newline at end of file
diff --git a/R/GMLOperationParameterGroup.R b/R/GMLOperationParameterGroup.R
new file mode 100644
index 00000000..b39838cf
--- /dev/null
+++ b/R/GMLOperationParameterGroup.R
@@ -0,0 +1,82 @@
+#' GMLOperationParameterGroup
+#'
+#' @docType class
+#' @importFrom R6 R6Class
+#' @export
+#' @keywords ISO GML operation parameter group
+#' @return Object of \code{\link{R6Class}} for modelling an GMLOperationParameterGroup
+#' @format \code{\link{R6Class}} object.
+#'
+#' @field maximumOccurs
+#' @field parameter
+#'
+#' @section Inherited methods from \code{GMLAbstractGeneralOperationParameter}
+#'
+#' @section Methods:
+#' \describe{
+#'  \item{\code{new(xml, defaults, id)}}{
+#'    This method is used to instantiate a GML OperationParameterGroup
+#'  }
+#'  \item{\code{setMaximumOccurs(maximumOccurs)}}{
+#'    Sets the maximum occurs, object of class \code{integer}
+#'  }
+#'  \item{\code{addParameter(parameter)}}{
+#'    Adds a parameter or parameter group, object of class \code{GMLOperationParameter}
+#'    or \code{GMLOperationParameterGroup}
+#'  }
+#'  \item{\code{delParameter(parameter)}}{
+#'    Deletes a parameter or parameter group, object of class \code{GMLOperationParameter}
+#'    or \code{GMLOperationParameterGroupo}
+#'  }
+#' }
+#' 
+#' @references 
+#'   ISO 19136:2007 Geographic Information -- Geographic Markup Language.
+#'   http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=32554 
+#'   
+#'   OGC Geography Markup Language. http://www.opengeospatial.org/standards/gml
+#' 
+#' @author Emmanuel Blondel <emmanuel.blondel1@@gmail.com>
+#'
+GMLOperationParameterGroup <- R6Class("GMLOperationParameterGroup",
+   inherit = GMLAbstractGeneralOperationParameter,
+   private = list(
+     xmlElement = "OperationParameterGroup",
+     xmlNamespacePrefix = "GML"
+   ),
+   public = list(
+     
+     #+ maximumOccurs [0..1]: integer
+     maximumOccurs = NULL,
+     #+ parameter [2..*]: GMLOperationParameter / GMLOperationParameterGroup
+     parameter = list(),
+     
+     #setMaximumOccurs
+     setMaximumOccurs = function(maximumOccurs){
+       if(!is(maximumOccurs, "integer")){
+         maximumOccurs <- as.integer(maximumOccurs)
+         if(is.na(maximumOccurs)){
+           stop("The argument value should be an object of class 'integer'")
+         }
+       }
+       self$maximumOccurs <- GMLElement$create("maximumOccurs", value = maximumOccurs)
+     },
+     
+     #addParameter
+     addParameter = function(param){
+       if(!inherits(param, "GMLAbstractGeneralOperationParameter")){
+         stop("The argument value should be an object of class 'GMLOperationParameter' or 'GMLOperationParameterGroup'")
+       }
+       return(self$addListElement("parameter", GMLElement$create("parameter", value = param)))
+     },
+     
+     #delParameter
+     delParameter = function(param){
+       if(!inherits(param, "GMLAbstractGeneralOperationParameter")){
+         stop("The argument value should be an object of class 'GMLOperationParameter' or 'GMLOperationParameterGroup'")
+       }
+       return(self$delListElement("parameter", GMLElement$create("parameter", value = param)))
+     }
+     
+   )
+)
\ No newline at end of file
diff --git a/man/GMLAbstractGeneralOperationParameter.Rd b/man/GMLAbstractGeneralOperationParameter.Rd
new file mode 100644
index 00000000..386ba11b
--- /dev/null
+++ b/man/GMLAbstractGeneralOperationParameter.Rd
@@ -0,0 +1,52 @@
+% Generated by roxygen2 (4.1.1): do not edit by hand
+% Please edit documentation in R/GMLAbstractGeneralOperationParameter.R
+\docType{class}
+\name{GMLAbstractGeneralOperationParameter}
+\alias{GMLAbstractGeneralOperationParameter}
+\title{GMLAbstractGeneralOperationParameter}
+\format{\code{\link{R6Class}} object.}
+\usage{
+GMLAbstractGeneralOperationParameter
+}
+\value{
+Object of \code{\link{R6Class}} for modelling an GMLAbstractGeneralOperationParameter
+}
+\description{
+GMLAbstractGeneralOperationParameter
+}
+\section{Fields}{
+
+\describe{
+\item{\code{minimumOccurs}}{}
+}}
+\section{Inherited methods from \code{GMLDefinition}}{
+
+}
+
+\section{Methods}{
+
+\describe{
+ \item{\code{new(xml, defaults, id)}}{
+   This method is used to instantiate a GML AbstractGeneralOperationParameter
+ }
+ \item{\code{setMinimumOccurs(minimumOccurs)}}{
+   Sets the minimum occurs, object of class \code{integer}
+ }
+}
+}
+\author{
+Emmanuel Blondel <emmanuel.blondel1@gmail.com>
+}
+\references{
+ISO 19136:2007 Geographic Information -- Geographic Markup Language.
+  http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=32554
+
+  OGC Geography Markup Language. http://www.opengeospatial.org/standards/gml
+}
+\keyword{GML}
+\keyword{ISO}
+\keyword{abstract}
+\keyword{general}
+\keyword{operation}
+\keyword{parameter}
+
diff --git a/man/GMLOperationMethod.Rd b/man/GMLOperationMethod.Rd
new file mode 100644
index 00000000..a69d8e44
--- /dev/null
+++ b/man/GMLOperationMethod.Rd
@@ -0,0 +1,68 @@
+% Generated by roxygen2 (4.1.1): do not edit by hand
+% Please edit documentation in R/GMLOperationMethod.R
+\docType{class}
+\name{GMLOperationMethod}
+\alias{GMLOperationMethod}
+\title{GMLOperationMethod}
+\format{\code{\link{R6Class}} object.}
+\usage{
+GMLOperationMethod
+}
+\value{
+Object of \code{\link{R6Class}} for modelling an GMLOperationMethod
+}
+\description{
+GMLOperationMethod
+}
+\section{Fields}{
+
+\describe{
+\item{\code{formulaCitation}}{}
+
+\item{\code{sourceDimensions}}{}
+
+\item{\code{targetDimensions}}{}
+}}
+\section{Inherited methods from \code{GMLDefinition}}{
+
+}
+
+\section{Methods}{
+
+\describe{
+ \item{\code{new(xml, defaults, id)}}{
+   This method is used to instantiate a GML OperationMethod
+ }
+ \item{\code{setFormulaCitation(citation)}}{
+   Sets the formula citation, object of class \code{ISOCitation}
+ }
+ \item{\code{setSourceDimensions(value)}}{
+   Sets the number of source dimensions, object of class \code{integer}
+ }
+ \item{\code{setTargetDimensions(value)}}{
+   Sets the number of target dimensions, object of class \code{integer}
+ }
+ \item{\code{addParameter(parameter)}}{
+   Adds a parameter or parameter group, object of class \code{GMLOperationParameter}
+   or \code{GMLOperationParameterGroup}
+ }
+ \item{\code{delParameter(parameter)}}{
+   Deletes a parameter or parameter group, object of class \code{GMLOperationParameter}
+   or \code{GMLOperationParameterGroupo}
+ }
+}
+}
+\author{
+Emmanuel Blondel <emmanuel.blondel1@gmail.com>
+}
+\references{
+ISO 19136:2007 Geographic Information -- Geographic Markup Language.
+  http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=32554
+
+  OGC Geography Markup Language. http://www.opengeospatial.org/standards/gml
+}
+\keyword{GML}
+\keyword{ISO}
+\keyword{method}
+\keyword{operation}
+
diff --git a/man/GMLOperationParameter.Rd b/man/GMLOperationParameter.Rd
new file mode 100644
index 00000000..b9e79242
--- /dev/null
+++ b/man/GMLOperationParameter.Rd
@@ -0,0 +1,42 @@
+% Generated by roxygen2 (4.1.1): do not edit by hand
+% Please edit documentation in R/GMLOperationParameter.R
+\docType{class}
+\name{GMLOperationParameter}
+\alias{GMLOperationParameter}
+\title{GMLOperationParameter}
+\format{\code{\link{R6Class}} object.}
+\usage{
+GMLOperationParameter
+}
+\value{
+Object of \code{\link{R6Class}} for modelling an GMLOperationParameter
+}
+\description{
+GMLOperationParameter
+}
+\section{Inherited methods from \code{GMLAbstractGeneralOperationParameter}}{
+
+}
+
+\section{Methods}{
+
+\describe{
+ \item{\code{new(xml, defaults, id)}}{
+   This method is used to instantiate a GML OperationParameter
+ }
+}
+}
+\author{
+Emmanuel Blondel <emmanuel.blondel1@gmail.com>
+}
+\references{
+ISO 19136:2007 Geographic Information -- Geographic Markup Language.
+  http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=32554
+
+  OGC Geography Markup Language. http://www.opengeospatial.org/standards/gml
+}
+\keyword{GML}
+\keyword{ISO}
+\keyword{operation}
+\keyword{parameter}
+
diff --git a/man/GMLOperationParameterGroup.Rd b/man/GMLOperationParameterGroup.Rd
new file mode 100644
index 00000000..a7a8e01e
--- /dev/null
+++ b/man/GMLOperationParameterGroup.Rd
@@ -0,0 +1,61 @@
+% Generated by roxygen2 (4.1.1): do not edit by hand
+% Please edit documentation in R/GMLOperationParameterGroup.R
+\docType{class}
+\name{GMLOperationParameterGroup}
+\alias{GMLOperationParameterGroup}
+\title{GMLOperationParameterGroup}
+\format{\code{\link{R6Class}} object.}
+\usage{
+GMLOperationParameterGroup
+}
+\value{
+Object of \code{\link{R6Class}} for modelling an GMLOperationParameterGroup
+}
+\description{
+GMLOperationParameterGroup
+}
+\section{Fields}{
+
+\describe{
+\item{\code{maximumOccurs}}{}
+
+\item{\code{parameter}}{}
+}}
+\section{Inherited methods from \code{GMLAbstractGeneralOperationParameter}}{
+
+}
+
+\section{Methods}{
+
+\describe{
+ \item{\code{new(xml, defaults, id)}}{
+   This method is used to instantiate a GML OperationParameterGroup
+ }
+ \item{\code{setMaximumOccurs(maximumOccurs)}}{
+   Sets the maximum occurs, object of class \code{integer}
+ }
+ \item{\code{addParameter(parameter)}}{
+   Adds a parameter or parameter group, object of class \code{GMLOperationParameter}
+   or \code{GMLOperationParameterGroup}
+ }
+ \item{\code{delParameter(parameter)}}{
+   Deletes a parameter or parameter group, object of class \code{GMLOperationParameter}
+   or \code{GMLOperationParameterGroupo}
+ }
+}
+}
+\author{
+Emmanuel Blondel <emmanuel.blondel1@gmail.com>
+}
+\references{
+ISO 19136:2007 Geographic Information -- Geographic Markup Language.
+  http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=32554
+
+  OGC Geography Markup Language. http://www.opengeospatial.org/standards/gml
+}
+\keyword{GML}
+\keyword{ISO}
+\keyword{group}
+\keyword{operation}
+\keyword{parameter}
+
diff --git a/tests/testthat/test_GMLOperationParameter.R b/tests/testthat/test_GMLOperationParameter.R
new file mode 100644
index 00000000..2f0c706d
--- /dev/null
+++ b/tests/testthat/test_GMLOperationParameter.R
@@ -0,0 +1,85 @@
+# test_GMLOperationParameter.R
+# Author: Emmanuel Blondel <emmanuel.blondel1@gmail.com>
+#
+# Description: Unit tests for GMLOperationParameter.R
+#=======================
+require(geometa, quietly = TRUE)
+require(testthat)
+require(XML)
+
+context("GMLAstractGeneralOperationParameter")
+
+test_that("GMLAbstractGeneralOperationParameter",{
+  
+  #encoding
+  gml <- GMLAbstractGeneralOperationParameter$new()
+  gml$setDescriptionReference("someref")
+  gml$setIdentifier("identifier", "codespace")
+  gml$addName("name1", "codespace")
+  gml$addName("name2", "codespace")
+  gml$setMinimumOccurs(2L)
+  xml <- gml$encode(validate=F)
+  expect_is(xml, "XMLInternalNode")
+  #decoding
+  gml2 <- GMLAbstractGeneralOperationParameter$new(xml = xml)
+  xml2 <- gml2$encode(validate=F)
+  #identity
+  expect_true(ISOAbstractObject$compare(gml, gml2))
+  
+})
+
+test_that("GMLOperationParameter",{
+  
+  #encoding
+  gml <- GMLOperationParameter$new()
+  gml$setDescriptionReference("someref")
+  gml$setIdentifier("identifier", "codespace")
+  gml$addName("name1", "codespace")
+  gml$addName("name2", "codespace")
+  gml$setMinimumOccurs(2L)
+  xml <- gml$encode()
+  expect_is(xml, "XMLInternalNode")
+  #decoding
+  gml2 <- GMLOperationParameter$new(xml = xml)
+  xml2 <- gml2$encode()
+  #identity
+  expect_true(ISOAbstractObject$compare(gml, gml2))
+  
+})
+
+test_that("GMLOperationParameterGroup",{
+  
+  #encoding
+  gml <- GMLOperationParameterGroup$new()
+  gml$setDescriptionReference("someref")
+  gml$setIdentifier("identifier", "codespace")
+  gml$addName("name1", "codespace")
+  gml$addName("name2", "codespace")
+  gml$setMinimumOccurs(2L)
+  gml$setMaximumOccurs(4L)
+  
+  param1 <- GMLOperationParameter$new(id = "ID1")
+  param1$setDescriptionReference("someref")
+  param1$setIdentifier("identifier", "codespace")
+  param1$addName("name1", "codespace")
+  param1$addName("name2", "codespace")
+  param1$setMinimumOccurs(2L)
+  gml$addParameter(param1)
+  
+  param2 <- GMLOperationParameter$new(id = "ID2")
+  param2$setDescriptionReference("someref")
+  param2$setIdentifier("identifier", "codespace")
+  param2$addName("name1", "codespace")
+  param2$addName("name2", "codespace")
+  param2$setMinimumOccurs(2L)
+  gml$addParameter(param2)
+  
+  xml <- gml$encode()
+  expect_is(xml, "XMLInternalNode")
+  #decoding
+  gml2 <- GMLOperationParameterGroup$new(xml = xml)
+  xml2 <- gml2$encode()
+  #identity
+  expect_true(ISOAbstractObject$compare(gml, gml2))
+  
+})
\ No newline at end of file