Patent Publication Number: US-7725503-B2

Title: System and method for unknown type serialization

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This is a continuation application and claims priority to U.S. patent application Ser. No. 10/383,666, filed Mar. 7, 2003, entitled “System and Method for Unknown Type Serialization,” which is hereby incorporated by reference in its entirety. 

   COPYRIGHT NOTICE/PERMISSION 
   A portion of the disclosure of this patent document contains material, which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever. The following notice applies to the software and data as described below and in the drawings hereto: Copyright © 2003, Microsoft Corporation, All Rights Reserved. 
   FIELD OF THE INVENTION 
   This invention relates in general to the field of distributed systems and frameworks. More particularly, this invention relates to a system and method of serialization of object data that also provides for the serialization of unknown data types in a strongly typed model. 
   BACKGROUND OF THE INVENTION 
   The process of serialization is the converting of an object or a connected graph of objects, stored within computer memory, and conventionally drawn on paper in two dimensions, into a linear encoded sequence of bytes. The basic idea of serialization is that an object should be able to write its current state, usually indicated by the value of its member variables, to persistent storage. The linear encoded bytes contain all of the information that was contained in the starting objects. That sequence of bytes may be used in several ways. For example, the sequence may be sent to another process on the same machine to construct arguments to a method that is run in another process. The sequence may be sent to the clipboard to be browsed or included in another application, sent “down the wire” to another machine to create a clone on that machine of the original object graph, or sent to a file on-disk so that it can be reused later. 
   The Microsoft .NET Framework accomplishes serialization by reflecting upon the object graph to generate a linear encoding (e.g., such as XML (Extensible Markup Language) or .NET Binary Format). Reflection allows the dynamic discovery of fields and properties for a given Common Language Runtime (CLR) type. Using reflection it is possible to retrieve the values of fields and properties from an object instance. Furthermore, reflection enables the developer to discern a type&#39;s inheritance hierarchy. 
   Deserialization is the process of taking the linear encoded representation of an object graph and re-hydrating the representation into an in-memory representation. The linear encoding contains a type description for each object in the graph. This type description is read and correlated with a CLR type. This CLR type is then instantiated and the data members are populated through reflection. By combining deserialization and serialization it is possible to transmit in-memory objects between endpoints in a distributed system. 
   Strongly-typed models are those where each type of data (e.g., integer, character, hexadecimal, packed decimal, user-defined types, etc.) is predefined within a type system that can be checked at compile-time by the compiler of a programming language (i.e., C/C++, C#, etc.) and all constants or variables defined for a given program must be described with one of the data types. A problem that often occurs within strongly typed models is that not all types are present on all nodes in the network. This problem could result because either the type is completely unknown or has been extended in a future version which is not available when deserializing the graph. 
   Thus, in view of the foregoing, there is a need for systems and methods that overcome the limitations and drawbacks of the prior art. In particular, there is a need to handle unknown types in a strongly typed distributed programming model. Further, there is a need for versioning and extensibility mechanisms in distributed models to allow different versions of systems to interoperate. The present invention provides such a solution. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to serializing and deserializing unknown data types in a strongly typed model. In accordance with an aspect of the invention, there is provided a method of deserializing a data stream. The method includes receiving the data stream, determining data types within the data stream, instantiating objects in accordance with known data types, and creating an unknown object to retain information related to an unknown data type in the data stream. The unknown object is used to regenerate the unknown data type when a reserialization operation is performed on the unknown object. 
   In accordance with a feature of the invention, the deserialization process determines completely unknown objects, which do not have a known base class. The present invention also determines the most-refined known base class of the unknown data type from the deserialization context, and if base class deserialization is allowed, assigns the most-refined known base class to the unknown data type while still retaining information related to the unknown fields of the encountered actual type for use during reserialization. 
   According to another aspect of the invention, there is provided a method of serializing objects to a data stream at a node where at least one of the object types is unknown to the node. The method includes mapping between the programming language types and an XML Schema, creating an instance of an output stream, and if an object type was previously known to the node, then it is mapped to the XML schema from the object&#39;s class to the output stream. If the object type was not previously known by the node, then it is mapped to the XML schema from an unknown object to reconstitute the data stream received by the node as the output stream. 
   According to another aspect of the invention, there is provided a method for communicating serialized data between nodes in a distributed system having a strongly typed model. The method includes serializing an object to the data stream at first node, communicating the data stream to a second node, deserializing the data stream at the second node, determining data types within the data stream, instantiating objects in accordance with known data types, and creating an unknown object to retain information related to an unknown data type in the data stream. The unknown object is used to regenerate the unknown data type when a reserialization operation is performed at the second node on the unknown object. 
   Additional features and advantages of the invention will be made apparent from the following detailed description of illustrative embodiments that proceeds with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing summary, as well as the following detailed description of preferred embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings exemplary constructions of the invention; however, the invention is not limited to the specific methods and instrumentalities disclosed. In the drawings: 
       FIG. 1  is a block diagram showing an exemplary computing environment in which aspects of the invention may be implemented; 
       FIG. 2  is a flow chart of the deserialization process of the present invention; 
       FIG. 3  is a flow chart of the serialization process of the present invention; and 
       FIG. 4  illustrates the serialization/deserialization process of the present invention wherein the endpoints of the process are of differing versions. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   The present invention is directed to systems and methods that provide full-featured search capabilities to Internet businesses, without necessitating the design and implementation of their own search facility. 
   Exemplary Computing Environment 
     FIG. 1  illustrates an example of a suitable computing system environment  100  in which the invention may be implemented. The computing system environment  100  is only one example of a suitable computing environment and is not intended to suggest any limitation as to the scope of use or functionality of the invention. Neither should the computing environment  100  be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary operating environment  100 . 
   The invention is operational with numerous other general purpose or special purpose computing system environments or configurations. Examples of well known computing systems, environments, and/or configurations that may be suitable for use with the invention include, but are not limited to, personal computers, server computers, hand-held or laptop devices, multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, distributed computing environments that include any of the above systems or devices, and the like. 
   The invention may be described in the general context of computer-executable instructions, such as program modules, being executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. The invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network or other data transmission medium. In a distributed computing environment, program modules and other data may be located in both local and remote computer storage media including memory storage devices. 
   With reference to  FIG. 1 , an exemplary system for implementing the invention includes a general purpose computing device in the form of a computer  110 . Components of computer  110  may include, but are not limited to, a processing unit  120 , a system memory  130 , and a system bus  121  that couples various system components including the system memory to the processing unit  120 . The system bus  121  may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. By way of example, and not limitation, such architectures include Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA) local bus, and Peripheral Component Interconnect (PCI) bus (also known as Mezzanine bus). 
   Computer  110  typically includes a variety of computer readable media. Computer readable media can be any available media that can be accessed by computer  110  and includes both volatile and non-volatile media, removable and non-removable media. By way of example, and not limitation, computer readable media may comprise computer storage media and communication media. Computer storage media includes both volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer storage media includes, but is not limited to, Random Access Memory (RAM), Read-Only Memory (ROM), Electrically Erasable Programmable Read-Only Memory (EEPROM), and Compact Disc Read-Only Memory (CD-ROM), digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can accessed by computer  110  . Communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. Combinations of any of the above should also be included within the scope of computer readable media. 
   The system memory  130  includes computer storage media in the form of volatile and/or non-volatile memory such as ROM  131  and RAM  132 . A basic input/output system  133  (BIOS), containing the basic routines that help to transfer information between elements within computer  110 , such as during start-up, is typically stored in ROM  131 . RAM  132  typically contains data and/or program modules that are immediately accessible to and/or presently being operated on by processing unit  120 . By way of example, and not limitation,  FIG. 1  illustrates operating system  134 , application programs  135 , other program modules  136 , and program data  137 . 
   The computer  110  may also include other removable/non-removable, volatile/non-volatile computer storage media. By way of example only,  FIG. 1  illustrates a hard disk drive  141  that reads from or writes to non-removable, non-volatile magnetic media, a magnetic disk drive  151  that reads from or writes to a removable, non-volatile magnetic disk  152 , and an optical disk drive  155  that reads from or writes to a removable, non-volatile optical disk  156 , such as a CD-ROM or other optical media. Other removable/non-removable, volatile/non-volatile computer storage media that can be used in the exemplary operating environment include, but are not limited to, magnetic tape cassettes, flash memory cards, digital versatile disks, digital video tape, solid state RAM, solid state ROM, and the like. The hard disk drive  141  is typically connected to the system bus  121  through a non-removable memory interface such as interface  140 , and magnetic disk drive  151  and optical disk drive  155  are typically connected to the system bus  121  by a removable memory interface, such as interface  150 . 
   The drives and their associated computer storage media, discussed above and illustrated in  FIG. 1 , provide storage of computer readable instructions, data structures, program modules and other data for the computer  110 . In  FIG. 1 , for example, hard disk drive  141  is illustrated as storing operating system  144 , application programs  145 , other program modules  146 , and program data  147 . Note that these components can either be the same as or different from operating system  134 , application programs  135 , other program modules  136 , and program data  137 . Operating system  144 , application programs  145 , other program modules  146 , and program data  147  are given different numbers here to illustrate that, at a minimum, they are different copies. A user may enter commands and information into the computer  110  through input devices such as a keyboard  162  and pointing device  161 , commonly referred to as a mouse, trackball or touch pad. Other input devices (not shown) may include a microphone, joystick, game pad, satellite dish, scanner, or the like. These and other input devices are often connected to the processing unit  120  through a user input interface  160  that is coupled to the system bus, but may be connected by other interface and bus structures, such as a parallel port, game port or a universal serial bus (USB). A monitor  191  or other type of display device is also connected to the system bus  121  via an interface, such as a video interface  190 . In addition to the monitor, computers may also include other peripheral output devices such as speakers  197  and printer  196 , which may be connected through an output peripheral interface  195 . 
   The computer  110  may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer  180 . The remote computer  180  may be a personal computer, a server, a router, a network PC, a peer device or other common network node, and typically includes many or all of the elements described above relative to the computer  110 , although only a memory storage device  181  has been illustrated in  FIG. 1 . The logical connections depicted include a local area network (LAN)  171  and a wide area network (WAN)  173 , but may also include other networks. Such networking environments are commonplace in offices, enterprise-wide computer networks, intranets and the Internet. 
   When used in a LAN networking environment, the computer  110  is connected to the LAN  171  through a network interface or adapter  170 . When used in a WAN networking environment, the computer  110  typically includes a modem  172  or other means for establishing communications over the WAN  173 , such as the Internet. The modem  172 , which may be internal or external, may be connected to the system bus  121  via the user input interface  160 , or other appropriate mechanism. In a networked environment, program modules depicted relative to the computer  110 , or portions thereof, may be stored in the remote memory storage device. By way of example, and not limitation,  FIG. 1  illustrates remote application programs  185  as residing on memory device  181 . It will be appreciated that the network connections shown are exemplary and other means of establishing a communications link between the computers may be used. 
   Exemplary Distributed Computing Framework and Architecture Overview 
   The serialization model of present invention advantageously enables a serialization engine to gracefully handle unknown types in a strongly-typed model. The serialized stream may be encoded in XML, a compact binary representation, Simple Object Access Protocol (SOAP), etc. Those of ordinary skill in the art would recognize that serialization of objects transforms object data into a stream. The present invention takes advantage of the fact that the runtime metadata knows all field and property definitions for each object&#39;s layout in memory. Thus, it is possible to serialize objects automatically, without having to write code to serialize each field. 
   As used herein, a “type” describes a CLR type, and defines a data contract for a memory structure and methods which operate over the data. It is noted that the present invention is not limited to CLR types and can be extended to other runtime programming types. Types may extend other types through inheritance. For example, when type B extends type A, B acquires the data, properties, and methods from A. By virtue of inheritance, types can extend each other in a hierarchical fashion. In accordance with the present invention, if an unknown type is encountered, an error is not generated and the application is allowed to determine that it has encountered an unknown object and is free to use its known and unknown fields as deemed appropriate at run time. There are two forms of unknown types: completely unknown types and unknown types where one of the base classes is known. This behavior enables the creations of intermediaries who are unaware of the types and do not interact with them. The intermediaries only need to be able to pass the objects on to another endpoint. 
   Below is an example of how to perform serialization of a graph of objects having a root arraylist l to a FileStream. In accordance with the present invention, Serialization can take place with any stream (e.g., MemoryStream, NetStream, etc.), and is not limited to a FileStream. 
   
     
       
         
             
           
             
                 
             
           
          
             
               class SerializeExample{ 
             
             
               public static void Main(String[] args) 
             
             
               { 
             
          
         
         
             
             
          
             
                 
               ArrayList 1 = new ArrayList( ); 
             
             
                 
               for (int x=0; x&lt; 100; x++) { 
             
          
         
         
             
             
          
             
                 
               1.Add (x); 
             
          
         
         
             
             
             
          
             
                 
               } 
               // create the object graph 
             
             
                 
               FileStream s = 
               // create the filestream 
             
             
                 
               File.Create(“foo.bin”); 
             
             
                 
               BinaryFormatter b = 
               // create the BinaryFormatter 
             
             
                 
               new BinaryFormatter( ); 
             
             
                 
               b.Serialize(s, l); 
               // serialize the graph to the stream 
             
          
         
         
             
          
             
               } // end main 
             
             
               } // end class 
             
             
                 
             
          
         
       
     
   
   This next code then goes on to creates a clone of the graph by deserializing it. The root of the clone graph is called p: 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               using System; 
             
             
                 
               using System.IO; 
             
             
                 
               using System.Collections; 
             
             
                 
               using System.Serialization; 
             
             
                 
               using System.Serialization.Formatters.Binary; 
             
             
                 
               class DeSerialize{ 
             
             
                 
               public static void Main(String[] args) 
             
             
                 
               { 
             
          
         
         
             
             
             
          
             
                 
               FileStream s = 
               // open the filestream 
             
             
                 
               File.Open(“foo.bin”); 
             
             
                 
               BinaryFormatter b = new 
               // create the formatter 
             
             
                 
               BinaryFormatter( ); 
             
             
                 
               ArrayList p = (ArrayList) 
               // deserialize 
             
             
                 
               b.Deserialize(s); 
             
             
                 
               p.ToString( ); 
               // print out the new object graph 
             
          
         
         
             
             
          
             
                 
               } // end Main 
             
             
                 
               } // end Class DeSerialize 
             
             
                 
                 
             
          
         
       
     
   
   As noted above, a problem occurs when unknown types are serialized in a strongly typed distributed programming model. The present invention advantageously overcomes this limitation of the prior art by deserializing an unknown type in the XML (or binary) stream as the most refined known CLR type available. The invention also provides a process for including Unknown Type information, which allows the original XML (or binary) data to be generated when the object is reserialized. The invention thus enables distributed systems to be implemented in a robust and strongly typed manner because if an unknown type is encountered, deserialization may be performed and an error is not generated, and the application is allowed to determine that it has encountered an unknown object and is free to use its known and unknown fields as deemed appropriate at run time. 
   In accordance with the present invention, there are two forms of unknown types: (1) “completely unknown types” and (2) “unknown types.” Instances of “completely unknown types” are preferably represented with the UnknownObject class (described below). The UnknownObject contains the XML type of the object and the serialized fields as a list of name-value pairs. It may also contain additional information that may be needed to regenerate the same XML when serializing the UnknownObject once again. “Unknown types” are those where the base class is known, but however, the actual type of the object is unknown. In this case, the present invention assigns the base class to the unknown type and retains unknown fields in an UnknownSubType field of the class (described below). The UnknownSubType contains the information necessary to reserialize the unknown types into their original XML. 
   Consider the following example of a client requesting a song from a remote server. The server may know about the types PlayCommand and Song. 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               [SBSerializable] 
             
             
                 
               public class PlayCommand 
             
             
                 
               { 
             
          
         
         
             
             
          
             
                 
               public Song RequestedSong; 
             
          
         
         
             
             
          
             
                 
               } 
             
             
                 
               [SBSerializable, 
             
             
                 
                SBType(AllowBaseClassDeserialization=true)] 
             
             
                 
               public class Song 
             
             
                 
               { 
             
          
         
         
             
             
          
             
                 
               [SBUnknownSubType] 
             
             
                 
               protected UnknownSubType subTypeInfo; 
             
             
                 
               public string Title; 
             
          
         
         
             
             
          
             
                 
               } 
             
             
                 
                 
             
          
         
       
     
   
   In this example, however, the client is running a newer version of the software, and it will send a SongEx instance as the RequestedSong field in the PlayCommand to request a particular song to be played. SongEx is defined as follows: 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               [SBSerializable, 
             
             
                 
                SBType(AllowBaseClassDeserialization=true)] 
             
             
                 
               public class SongEx : Song 
             
             
                 
               { 
             
          
         
         
             
             
          
             
                 
               public string Album; 
             
          
         
         
             
             
          
             
                 
               } 
             
             
                 
                 
             
          
         
       
     
   
   When the server tries to deserialize a request from this client, it will determine that the RequestedSong field is occupied by a type called SongEx, which it does not know about. However, the server does know that the field is to be of type Song, and Song has been marked to indicate that it is acceptable to deserialize unknown types as the base class. As such, the deserialization engine will instantiate a Song and populates the known fields. It will also package up the unknown fields and unknown type name into an UnknownSubType object and assign it to the field decorated with SBUnknownSubTypeAttribute which in this case is the subTypeInfo field of the Song type. If the server ever reserializes the Song instance with the unknown type info, the serialization engine will use the UnknownSubType field to regenerate the original XML. 
     FIG. 2  is a flow chart illustrating the operation of the deserialization process of the present invention. At step  200 , serialized data is received by a node. At step  202  it is determined if the received type is unknown. If not, then at step  204 , the datastream is deserialized and the object represented thereby is instantiated. If the type is unknown at step  202 , then at step  206 , it is determined if a base class of the unknown type is known and if base deserialization is allowed. If so, then at step  208 , the unknown type is deserialized to a known base class and the unknown fields and unknown type name are packaged to an UnknownSubType object. If there is no base class for the unknown type at  206 , then at step  210  the type is deserialized to an UnknownObject object. The process is repeated until all the objects in the input stream have been deserialized. The result is an object graph in which some nodes might be represented by Unknown objects. 
   Referring back to the previous example, if Song does not allow base class deserialization, PlayCommand would be responsible for handling the unknown type. As such, the service is not able to convert the unknown SongEx into a Song, and an UnknownObject is created. Since the RequestedSong field is typed as a Song, the server would not be able to assign the UnknownObject to it. An unassignable field instance typically results in the deserialization operation failing. However, the PlayCommand may be rewritten to prevent this problem. For example, a first option is to use an Object field with an attribute specifying the actual type. 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               [SBSerializable] 
             
             
                 
               public class PlayCommand 
             
             
                 
               { 
             
          
         
         
             
             
          
             
                 
               [SBField( 
             
          
         
         
             
             
          
             
                 
               XmlElementName=“RequestedSong”, 
             
             
                 
               ActualType=typeof(Song))] 
             
          
         
         
             
             
          
             
                 
               private Object _song; 
             
             
                 
               public Song RequestedSong 
             
             
                 
               { 
             
          
         
         
             
             
          
             
                 
                get { return (Song)_song; } 
             
          
         
         
             
             
          
             
                 
               } 
             
          
         
         
             
             
          
             
                 
               } 
             
             
                 
                 
             
          
         
       
     
   
   In this case, a failure will not occur until an application attempts to retrieve the RequestedSong property. An invalid cast exception will be realized for trying to convert an UnknownObject into a Song. Of course, the above PlayCommand can be enhanced to gracefully handle the UnknownObject by looking for the “title” field and using it to play the requested song. 
   Another option is to provide a tracking field for unassignable types. In this case, when the server cannot assign an UnknownObject to the Song property, it will track the value within the FieldTrackingInfo field. When reserializing the object, the server will check FieldTrackingInfo for a value if the RequestedSong is null. 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               [SBSerializable] 
             
             
                 
               public class PlayCommand 
             
             
                 
               { 
             
          
         
         
             
             
          
             
                 
               [SBFieldTrackingInfo] 
             
             
                 
               protected FieldTrackingInfo FieldTrackingInfo; 
             
             
                 
               public Song RequestedSong; 
             
          
         
         
             
             
          
             
                 
               } 
             
             
                 
                 
             
          
         
       
     
   
   In all the above cases, the published XML contract for PlayCommand remains the same. 
   Referring to  FIG. 3 , to reserialize object including unknown objects, the present invention maps from the programming language constructs to, e.g., an XML Schema. An XML serializer maps between the CLR type and an XML Schema type (step  300 ). If an object type was previously known (step  302 ), the type is mapped to the XML schema from the object&#39;s class (step  304 ). If the object was not previously known, then the unknown aspects of the type is mapped to an instance of the UnknownSubType class or, if completely unknown, the UnknownObject class. Thus, unknown types encountered during the deserialization process can be reserialized to the original XML data stream in accordance with data preserved in UnknownObject and UnknownSubType. 
   The object classes implemented in present invention to handle the serialization of unknown types will now be discussed. It is noted that the objects described below are provided for exemplary purposes and are not intended to limit the scope of the present invention. 
   1. TypeHierarchy 
   TypeHierarchy is a class that holds a list of all types in the class hierarchy. This information is used to allow the deserializer to instantiate the most derived type for which it has an implementation. 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               public abstract class TypeHierarchy 
             
             
                 
               { 
             
          
         
         
             
             
          
             
                 
               public abstract XsdQName[] Hierarchy { get; } 
             
          
         
         
             
             
          
             
                 
               } 
             
             
                 
                 
             
          
         
       
     
   
   Hierarchy is a list of the types in the XML type hierarchy sorted from the most refined down to the base class that is an immediate child of CLR Object type (XML Schema Definition (XSD) anyType). 
   2. UnknownSubType 
   UnknownSubType is used for storing additional type information and unknown fields when deserializing an unknown type as a known base class. When a class indicates that it allows base class deserialization, it has a field of type UnknownSubType marked with the SBUnknownSubTypeAttribute. 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               public abstract class UnknownSubType 
             
             
                 
               { 
             
          
         
         
             
             
          
             
                 
               public abstract XsdQName ActualType { get; } 
             
             
                 
               public abstract TypeHierarchy Hierarchy { get; } 
             
             
                 
               public abstract int FieldCount { get; } 
             
             
                 
               public abstract UnknownField GetField(int index); 
             
             
                 
               public abstract UnknownField GetField( 
             
          
         
         
             
             
          
             
                 
               string fieldName); 
             
          
         
         
             
             
          
             
                 
               } 
             
             
                 
                 
             
          
         
       
     
   
   ActualType is the actual type of the object. This may be null if the actual type of the object could not be determined from the deserialized stream. Hierarchy stores the full type hierarchy of the object if the type hierarchy information was included when the instance was serialized. Normally, the property will be null indicating that no such information is needed. FieldCount returns the number of unknown fields present. GetField(int index) returns an unknown field given its index. GetField(string fieldName) returns an unknown field given its name. 
   3. UnknownObject 
   UnknownObject holds the state for objects of a completely unknown type. 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               public abstract class UnknownObject 
             
             
                 
               { 
             
          
         
         
             
             
          
             
                 
               public abstract XsdQName ActualType { get; } 
             
             
                 
               public abstract TypeHierarchy Hierarchy { get; } 
             
             
                 
               public abstract int FieldCount { get; } 
             
             
                 
               public abstract UnknownField GetField(int index); 
             
             
                 
               public abstract UnknownField GetField( 
             
          
         
         
             
             
          
             
                 
               string fieldName); 
             
          
         
         
             
             
          
             
                 
               } 
             
             
                 
                 
             
          
         
       
     
   
   The fields of the UnknownObject type are similar to that noted above with regard to UnknownSubType type. 
   4. UnknownField 
   UnknownField holds the state for an unknown field. 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               public abstract class UnknownField 
             
             
                 
               { 
             
          
         
         
             
             
          
             
                 
               public abstract string Name { get; } 
             
             
                 
               public abstract Object Value { get; set; } 
             
             
                 
               public abstract bool includeActualType { get; set; } 
             
             
                 
               public abstract bool IsSingleRef { get; set; } 
             
          
         
         
             
             
          
             
                 
               } 
             
             
                 
                 
             
          
         
       
     
   
   Name is the name of the unknown field. This name is encoded to be an XML element name. Value is the value of the unknown field. Field includeActualType, if true, means that the xsi:type (see, XML Schema Part 0: Primer, XML Schema Part 1: Structures, and XML Schema Part 2: Datatypes, W3C Recommendations, 2 May 2001, which are incorporated herein by referenced in their entireties) attribute must be included on the serialized element with this value. IsSingleRef indicates whether the field should be serialized as a single-reference element (see, Simple Object Access Protocol (SOAP) 1.1, W3C Note, 08 May 2000, which is incorporated herein by reference in its entirety). 
   5. UnknownPrimitiveValue 
   Within unknown types in a graph, the actual type of an unknown field can be either a simple-type (primitive) or a complex-type. The two cases are distinguished from the fact that simple-type has its value encoded as text values whereas complex-type has one or more sub-elements to represent the values of its fields. Thus, it can be inferred that the deserialization process recurses for complex-types with the recursion bottoming out when all the encountered fields are of simple-type. The type of simple-type field will not be known unless the element is decorated with an xsi:type attribute. For example, it is not possible to know whether a simple-type field is an integer or a string when using XML as the serialization format. Simple-type values whose type cannot be determined are stored as an UnknownPrimitiveValue instance which will appear as the Value property on an UnknownField. 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               public class UnknownPrimitiveValue 
             
             
                 
               { 
             
          
         
         
             
             
          
             
                 
               XsdQName ActualType { get; } 
             
             
                 
               public string Value { get; } 
             
          
         
         
             
             
          
             
                 
               } 
             
             
                 
                 
             
          
         
       
     
   
   6. PossibleQNameValue 
   For some unknown values, it is possible that they might be a QName. In order to properly reserialize the XML data, the XML namespace and prefix that would apply if the unknown value happens to actually be a QName must be retained. This requires special handling because it is the only XML type whose actual value is dependent on the containing XML document. 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               public class PossibleQNameValue : UnknownPrimitiveValue 
             
             
                 
               { 
             
          
         
         
             
             
          
             
                 
               public string Prefix { get; } 
             
             
                 
               public string Namespace { get; } 
             
          
         
         
             
             
          
             
                 
               } 
             
             
                 
                 
             
          
         
       
     
   
   7. UnknownArray 
   Arrays of unknown types require special handling and are represented with the UnknownArray class. 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               public abstract class UnknownArray 
             
             
                 
               { 
             
          
         
         
             
             
          
             
                 
               public abstract XsdQName ElementType { get; } 
             
             
                 
               public abstract int Rank { get; } 
             
             
                 
               public abstract int GetSize(int dimension); 
             
             
                 
               public abstract void SetValue(Object obj, int index); 
             
             
                 
               public abstract void SetValue( 
             
          
         
         
             
             
          
             
                 
               Object obj, int[] indices); 
             
          
         
         
             
             
          
             
                 
               public abstract Object GetValue(int index); 
             
             
                 
               public abstract Object GetValue(int[] indices); 
             
          
         
         
             
             
          
             
                 
               } 
             
             
                 
                 
             
          
         
       
     
   
   ElementType is the element type of the array. Rank is the number of dimensions in the array. GetSize(int dimension) Returns the size of the specified dimension. SetValue(Object obj, int index) Sets the array value at the specified index. SetValue(Object obj, int[ ] indices) sets the array value at the specified indices. GetValue(int index) gets the array value at the specified index. GetValue(int[ ] indices) gets the array value at the specified indices. 
   8. UnknownJaggedArray 
   UnknownJaggedArray represents a jagged array with an unknown base type. The “values” of this array will be the child arrays. 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               public abstract class UnknownJaggedArray : UnknownArray 
             
             
                 
               { 
             
          
         
         
             
             
          
             
                 
               public abstract int ChildLevels { get; } 
             
             
                 
               public abstract int GetChildLevelRank(int index); 
             
          
         
         
             
             
          
             
                 
               } 
             
             
                 
                 
             
          
         
       
     
   
   ChildLevels indicates the number of child levels in the array. GetChildLevelRank(int index) returns the rank of the jagged array at the given child level. 
     FIG. 4  illustrates an exemplary embodiment of the present invention wherein two endpoints  400  and  402  are running different versions of an operating system. In the exemplary embodiment, endpoint  400  is a newer version than endpoint  402 . When the object graph illustrated at endpoint  400  is serialized (Step  1 ) the resulting XML data  404  is generated. The XML data  404  is the forwarded to endpoint  402  and deserialized (Step  2 ). As illustrated, the endpoint  402  does not know about certain types (e.g., MusicCD). As such, it deserializes the unknown subtype MusicCD into appropriate unknown classes (UnknownSubType, UnknownField, UnknownPrimitiveValue). It is noted that  FIG. 4  that the UnknownField instance associated with the “hash” field of the “Class MusicCD” is not illustrated. This field is stored in memory, however, not shown in the FIG. for the sole purpose of simplifying the FIG. In accordance with the present invention, when the endpoint  204  reserializes the object graph (Step  3 ), the XML data  404  can be recreated. If necessary, this can be deserialized (Step  4 ) at the endpoint  400  into the original object graph that was serialized at Step  1 . 
   As has been described above, the present invention through its unique deserialization/serialization method, enables intermediaries that typically lack knowledge of the types being exchanged by the endpoints to be placed in between them. It also enables different versions of endpoints that have evolved independently to interoperate. 
   While the present invention has been described in connection with the preferred embodiments of the various FIGS., it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. For example, one skilled in the art will recognize that the present invention as described in the present application may apply to any computing device or environment, whether wired or wireless, may be applied to a serialization format other than XML, and may be applied to any number of such computing devices connected via a communications network, and interacting across the network. Furthermore, it should be emphasized that a variety of computer platforms, including handheld device operating systems and other application specific operating systems are contemplated, especially as the number of wireless networked devices continues to proliferate. Still further, the present invention may be implemented in or across a plurality of processing chips or devices, and storage may similarly be effected across a plurality of devices. Therefore, the present invention should not be limited to any single embodiment, but rather should be construed in breadth and scope in accordance with the appended claims.