diff --git a/src/pv/pvaClient.h b/src/pv/pvaClient.h
index 2107726..aba39cd 100644
--- a/src/pv/pvaClient.h
+++ b/src/pv/pvaClient.h
@@ -17,6 +17,7 @@
 
 #include <list>
 #include <iostream>
+#include <ostream>
 #include <sstream>  
 #include <pv/requester.h>
 #include <pv/status.h>
@@ -613,6 +614,7 @@ public:
     void setData(
         epics::pvData::PVStructurePtr const & pvStructureFrom,
         epics::pvData::BitSetPtr const & bitSetFrom);
+
     /** @brief Is there a top level field named value.
      * @return The answer.
      */
@@ -679,6 +681,29 @@ public:
      * @return The timeStamp.
      */
     epics::pvData::TimeStamp getTimeStamp();
+    /** @brief parse from args
+     *
+     * Accepts arguments of the form json or field='value' where value is json syntax.
+     * field is name.name...
+     * @param args The arguments
+     * @throw runtime_error if failure.
+     */
+    void parse(const std::vector<std::string> &args);
+    /** @brief generate JSON output from the current PVStructure
+     *
+     * @param strm output stream
+     * @param ignoreUnprintable false or true; default is true.
+     * @param multiline false or true; default is false
+     *
+     * @throw runtime_error if failure.
+     */
+    void streamJSON(
+               std::ostream& strm,
+               bool ignoreUnprintable = true,
+               bool multiLine = false);
+     /** @brief set length of all array fields to 0
+     */
+    void zeroArrayLength();
     /** @brief Factory method for creating an instance of PvaClientData.
      *
      * NOTE: Not normally called by clients
@@ -691,12 +716,19 @@ protected:
     void checkValue();
     std::string messagePrefix;
 private:
+    void parse(
+        const std::string &arg,
+        const epics::pvData::PVFieldPtr &dest,
+        epics::pvData::BitSetPtr &bitSet);
+    void parse(
+        const std::string &arg,
+        const epics::pvData::PVUnionPtr &dest);
+    void zeroArrayLength(const epics::pvData::PVStructurePtr &pvStructure);
 
     epics::pvData::StructureConstPtr structure;
     epics::pvData::PVStructurePtr pvStructure;
     epics::pvData::BitSetPtr bitSet;
 
-    
     epics::pvData::PVFieldPtr pvValue;
     epics::pvData::PVAlarm pvAlarm;
     epics::pvData::PVTimeStamp pvTimeStamp;
diff --git a/src/pvaClientData.cpp b/src/pvaClientData.cpp
index 5db266d..b503732 100644
--- a/src/pvaClientData.cpp
+++ b/src/pvaClientData.cpp
@@ -11,9 +11,17 @@
 
 #include <typeinfo>
 #include <sstream>
+#include <istream>
+#include <ostream>
 
 #include <pv/createRequest.h>
 #include <pv/convert.h>
+#include <pv/pvEnumerated.h>
+
+#if EPICS_VERSION_INT>=VERSION_INT(3,15,0,1)
+#  include <pv/json.h>
+#  define USE_JSON
+#endif
 
 #define epicsExportSharedSymbols
 
@@ -106,6 +114,7 @@ void PvaClientData::setData(
    pvValue = pvStructure->getSubField("value");
 }
 
+
 bool PvaClientData::hasValue()
 {
     if(PvaClient::getDebug()) cout << "PvaClientData::hasValue\n";
@@ -358,4 +367,141 @@ TimeStamp PvaClientData::getTimeStamp()
    throw std::runtime_error(messagePrefix + noTimeStamp);
 }
 
+void PvaClientData::zeroArrayLength()
+{
+    if(!pvStructure) throw new std::runtime_error(messagePrefix + noStructure);
+    zeroArrayLength(pvStructure);
+}
+void PvaClientData::parse(
+    const std::string &arg,const PVFieldPtr &dest,BitSetPtr & bitSet)
+{
+#ifdef USE_JSON
+    std::istringstream strm(arg);
+    parseJSON(strm, dest,&(*bitSet));
+#else
+    throw std::runtime_error("JSON support not built");
+#endif
+}
+
+void PvaClientData::parse(
+    const std::string &arg,const PVUnionPtr &pvUnion)
+{
+    if(pvUnion->getUnion()->isVariant()) {
+          throw std::runtime_error(messagePrefix + "varient union not implemented");
+    }
+    size_t iequals = arg.find_first_of('=');
+    string field;
+    string rest;
+    if(iequals==std::string::npos) {
+        string mess(arg);
+        mess += " was expected to start with field=";
+          throw std::runtime_error(messagePrefix + mess);
+    }
+    field = arg.substr(0,iequals);
+    rest = arg.substr(iequals+1);
+    PVFieldPtr pvField(pvUnion->select(field));
+    if(pvField->getField()->getType()==epics::pvData::union_) {
+        PVUnionPtr pvu = static_pointer_cast<PVUnion>(pvField);
+        parse(rest,pvu);
+        return;
+    }
+    BitSetPtr bs;
+    parse(rest,pvField,bs);
+    return;
+}
+
+void PvaClientData::parse(const std::vector<std::string> &args)
+{
+    if(!pvStructure) throw std::runtime_error(messagePrefix + noStructure);
+    if(!bitSet) throw std::runtime_error(messagePrefix + noStructure);
+    size_t num = args.size();
+    if(num<1) throw std::runtime_error(messagePrefix + " no arguments");
+    for(size_t i=0; i<num; ++i)
+    {
+        string val = args[i];
+        size_t iequals = val.find_first_of('=');
+        string field;
+        string rest(val);
+        if(iequals==std::string::npos) {
+           parse(rest,pvStructure,bitSet);
+           continue;
+        }
+        field = val.substr(0,iequals);
+        rest = val.substr(iequals+1);
+        if(field.size()==std::string::npos) {
+           parse(rest,pvStructure,bitSet);
+           continue;
+        } 
+        PVFieldPtr pvField(pvStructure->getSubField(field));
+        // look for enumerated structure
+        PVEnumerated pvEnumerated;
+        bool result = pvEnumerated.attach(pvField);
+        if(result) {
+             PVStringArray::const_svector choices(pvEnumerated.getChoices());
+             for(size_t i=0; i<choices.size(); ++i) {
+                  if(choices[i]==rest) {
+                     pvEnumerated.setIndex(i);
+                     return;
+                  }
+             }
+        }
+        // look for union
+        PVUnionPtr pvUnion(pvStructure->getSubField<PVUnion>(field));
+        if(pvUnion) {
+            parse(rest,pvUnion);
+            bitSet->set(pvUnion->getFieldOffset());
+            return;
+        }
+        parse(rest,pvField,bitSet);
+    }
+}
+
+void PvaClientData::streamJSON(
+               std::ostream& strm,
+               bool ignoreUnprintable,
+               bool multiLine)
+{
+#ifdef USE_JSON
+    JSONPrintOptions opts;
+    opts.ignoreUnprintable = ignoreUnprintable;
+    opts.multiLine = multiLine;
+    printJSON(strm,*pvStructure,*bitSet,opts);
+#else
+    throw std::runtime_error("JSON support not built");
+#endif
+}
+
+
+void PvaClientData::zeroArrayLength(const epics::pvData::PVStructurePtr &pvStructure)
+{
+const PVFieldPtrArray pvFields(pvStructure->getPVFields());
+    for(size_t i=0; i<pvFields.size(); ++i) {
+        PVFieldPtr pvField = pvFields[i];
+        Type type(pvField->getField()->getType());
+        switch(type) {
+        case epics::pvData::scalarArray:
+            {
+                PVScalarArrayPtr pvScalarArray = static_pointer_cast<PVScalarArray>(pvField);
+                pvScalarArray->setLength(0);
+            }
+            break;
+        case epics::pvData::structureArray:
+            {
+                PVStructureArrayPtr pvStructureArray = static_pointer_cast<PVStructureArray>(pvField);
+                pvStructureArray->setLength(0);
+            }
+            break;
+        case epics::pvData::structure:
+            {
+                PVStructurePtr pvStructure = static_pointer_cast<PVStructure>(pvField);
+                zeroArrayLength(pvStructure);
+            } 
+            break;
+        default:
+               break;
+        }
+    }
+}
+
+
 }}