- "Permanent storage devices of conventional computer systems are arranged
in a hierarchical fashion. This hierarchy is formed through the use of
directories or folders. A folder is a logical grouping of files and
other folders. When a user
wishes to store information on the permanent storage device of a
computer system, the user creates a folder and moves, copies, or
creates files in the folder. The functionality associated with a folder
is typically defined by a computer system. This
functionality may include simply adding and deleting files of a folder.
Thus, in conventional computer systems, the user has little control
over the functionality of the folder. For example, a user cannot
typically restrict the types of files that are
stored in a folder nor can a user modify a folder so that all users
must observe a checkin-checkout protocol when accessing the files in
the folder.
The present invention is described below using some object-oriented techniques; thus, an overview of well-known object-oriented programming techniques is provided. Two common characteristics of object-oriented programming languages are support for data encapsulation and data type inheritance. Data encapsulation refers to the binding of functions and data. Inheritance refers to the ability to declare a data type in terms of other data types. In the C++ language, data encapsulation and inheritance are supported through the use of classes. A class is a user-defined type. A class declaration describes the data members and function members of the class. A function member is also referred to as a method of a class. The data members and function members of a class are bound together in that the function operates on an instance of the class. An instance of a class is also called an object of the class. Thus, a class provides a definition for a group of objects with similar properties and common behavior.
To allocate storage for an object of a particular type (class), an object is instantiated. Once instantiated, data can be assigned to the data members of the particular object. Also, once instantiated, the function members of the particular object can be invoked to access and manipulate the data members. Thus, in this manner, the function members implement the behavior of the object, and the object provides a structure for encapsulating data and behavior into a single entity.
To support the concept of inheritance, classes may be derived from (based upon the declaration of) other classes. A derived class is a class that inherits the characteristics--data members and function members--of its base classes. A class that inherits the characteristics of another class is a derived class. A class that does not inherit the characteristics of another class is a primary (root) class. A class whose characteristics are inherited by another class is a base class. A derived class may inherit the characteristics of several classes; that is, a derived class may have several base classes. This is referred to as multiple inheritance.
A class may also specify whether its function members are virtual. Declaring that a function member is virtual means that the function can be overridden by a function of the same name and type in a derived class. If a virtual function is declared without providing an implementation, then it is referred to as a pure virtual function. A pure virtual function is a virtual function declared with the pure specifier, "=0". If a class specifies a pure virtual function, then any derived class needs to specify an implementation for that function member before that function member may be invoked. A class which contains at least one pure virtual function member is an abstract class.
[Original image modified for size and/or readability]FIG. 1 is a block diagram illustrating typical data structures
used to represent an object. An object is composed of instance data
(data members) and function members, which implement the behavior of
the object. The data structures used to
represent an object comprise instance data structure 101, virtual
function table 102, and the function members 103, 104, 105. The
instance data structure 101 contains a pointer to the virtual function
table 102 and contains data members. The virtual
function table 102 contains an entry for each virtual function member
defined for the object. Each entry contains a reference to the code
that implements the corresponding function member. The layout of this
sample object conforms to models defined in
U.S. Pat. No. 5,297,284, entitled "A Method for Implementing Virtual
Functions and Virtual Bases in a Compiler for an Object Oriented
Programming Language," which is hereby incorporated by reference. In
the following, an object will be described as an
instance of a class as defined by the C++ programming language. One
skilled in the art would appreciate that other object models can be
defined using other programming languages.
An advantage of using object-oriented techniques is that these techniques can be used to facilitate the sharing of objects. For example, a program implementing the function members of an instantiated object (a "server program") can share the object with another program (a "client program"). To allow an object of an arbitrary class to be shared with a client program, interfaces are defined through which an object can be accessed without the need for the client program to have access to the class definitions at compile time. An interface is a named set of logically related function members ("methods) and data members ("properties"). In C++, an interface is an abstract class with no data members and whose virtual functions are all pure. Thus, an interface provides a published protocol for two programs to communicate. Interfaces are typically used for derivation: a program defines (implements) classes that provide implementations for the interfaces the classes are derived from. Thereafter, objects are created as instances of these derived classes. Objects instantiated from a derived class implementing particular interfaces are said to "support" the interfaces. An object supports one or more interfaces depending upon the desired functionality.
When a client program desires to share an object, the client program needs access to the code that implements the interfaces for the object (the derived class code). To access the derived class code (also referred to as class code), each class implementation is given a unique class identifier (a "CLSID"). For example, code implementing a spreadsheet object developed by Microsoft Corporation may have a class identifier of "MSSpreadsheet," while code implementing a spreadsheet object developed by another corporation may have a class identifier of "LTSSpreadsheet." A persistent registry in each computer system is maintained that maps each CLSID to the code that implements the class. Typically, when a spreadsheet program is installed on a computer system, the persistent registry is updated to reflect the availability of that class of spreadsheet objects. So long as a spreadsheet developer implements each function member defined by the interfaces to be supported by spreadsheet objects and so long as the persistent registry is maintained, the client program can access the function members of shared spreadsheet objects without regard to which server program has implemented them or how they have been implemented.
Since an object may support some interfaces and not others, a client program would need to determine at runtime whether a particular object supports a particular interface. To enable this determination, every object supports the interface IUnknown, which contains a function member, QueryInterface, that indicates which interfaces are implemented for the object. The method QueryInterface is defined as follows:
The method QueryInterface is passed an interface identifier in parameter iid (of type REFIID) and returns in parameter ppv a pointer to the implementation of the identified interface of the object for which the method is invoked. If the object does not support the interface, then the method returns a false. The type HRESULT indicates a predefined status.
[Original image modified for size and/or readability]FIG. 2 is a symbolic representation of an object. In the
following description, an object data structure is represented by the
shape 201 labeled with the interfaces through which the object may be
accessed .....
In accordance with a first aspect of the present invention, a method is executed in a distributed system having a Dumber (sic) of computer systems that are connected by a network. In accordance with this method of the first aspect of the present invention, at least one of the computers has a container for storing objects and links. This method provides for the programmability of the container. The programmability of the container is provided through replacing the methods of the container and extending the functionality of the container.
In accordance with a second aspect of the present invention, an improved storage mechanism is provided. The storage mechanism of the preferred embodiment provides for a programmable container. The container of the preferred embodiment contains methods that are replaceable as well as a command unit that extends the functionality of the container .....
A preferred embodiment of the present invention provides for an improved method and system for storing information in a computer system. In a preferred embodiment, information is stored through the use of a container. A container is an object that contains a collection of data ("contained objects") and that provides an interface through which to access the collection of data. The contained objects can include files, databases, electronic mail messages, bitmaps, other objects, other containers, and various other types of data. In the preferred embodiment, a container is programmable. This programmability is provided by allowing for replacement of the implementation of the interface of the container ("replaceability") and by allowing for the extension of the functionality provided by the interface ("extendibility"). Because containers are replaceable and extendible, the functionality of a container can be tailored to the needs of a user. For example, a user can extend the functionality of a container to limit the types of data that are stored within the container. Thus, containers are a more flexible storage mechanism than conventional folders."
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I am filing this entry in the Reference Library to this blog.