US 20050262138 A1
A family of Java interfaces defines methods to provide common information about a property, such as data type and editing capabilities. The interfaces identify the methods used to get generic metadata. Implementers may extend these classes, as needed, to provide the metadata for their specific properties. The common metadata description interface of the present invention allows multiple metadata sources to be used interchangeably within the same software product without the software code being specifically written for each metadata source.
10. A computer implemented method for providing metadata about a set of properties, comprising:
creating a first object describing metadata for a plurality of data sources, wherein the first object maintains a related set of properties; and
creating a set of second objects describing metadata for respective properties of the data sources;
wherein metadata concerning a respective property is obtained by invoking a method in the first object to identify the respective property, and then invoking a method in a respective one of the second objects to dynamically obtain the metadata concerning the respective property.
11. The method of
12. The method of
13. The method of
23. An apparatus embodied in a computer useable medium for defining metadata about a related set of properties, comprising:
a computer useable medium
a first object on the computer useable medium describing metadata for a plurality of data sources, wherein the first object maintains a related set of properties for the plurality of data sources; and
a set of second objects on the computer useable medium describing metadata for respective properties of the data sources that are maintained by the first object.
24. The apparatus of
25. The apparatus of
26. The apparatus of
30. A computer program product comprising:
a computer usable medium having computer usable program code for providing metadata about a set of properties, said computer program product including:
computer usable program code for creating a first object describing metadata for a plurality of data sources, wherein the first object maintains a related set of properties; and
computer usable program code creating a set of second objects describing metadata for respective properties of the data sources, wherein metadata concerning a respective property is obtained by invoking a method in the first object to identify the respective property, and then invoking a method in a respective one of the second objects to dynamically obtain the metadata concerning the respective property.
31. The computer program product of
32. The computer program product of
33. The computer program product of
1. Technical Field
The present invention relates to data processing and, in particular, to the definition of metadata in the Java programming language. Still more particularly, the present invention provides an open framework for the definition of metadata.
2. Description of Related Art
Java is a programming language designed to generate applications that can run on all hardware platforms without modification. Java is an interpreted language. The source code of a Java program is compiled into an intermediate language called “bytecode,” which cannot run by itself. The bytecode must be converted (interpreted) into machine code at runtime. Upon finding a Java applet, e.g., in a Web page, a Web browser invokes a Java interpreter (Java Virtual Machine (JVM)) which translates the bytecode into machine code and runs it. JVMs are available for most hardware platforms. Thus, Java programs are not dependent on any specific hardware and will run in any computer with the Java Virtual Machine software. On the server side, Java programs can also be compiled into machine language for fastest performance, but they lose their hardware independence as a result.
JavaBeans are a component software architecture that runs in the Java environment. JavaBeans are independent Java program modules that are called for and executed. They have been used primarily for developing user interfaces at the client side. The server-side counterpart is Enterprise JavaBeans (EJBs). Java programs may also reference data sources other than JavaBeans and EJBs. For example, a Java program may reference a database made up of tables. Each source of data may have a different associated metadata. Metadata is data that describes other data. Data dictionaries and repositories are examples of metadata.
With different metadata sources, programmers must anticipate every possible metadata source and write code to communicate properly with each metadata source. If code is written for a plurality of metadata sources, the code may become very complicated. Furthermore, it is impossible to anticipate new metadata formats in the future. If an enterprise wishes to add a new data type and, thus, a new metadata source, the code must be completely rewritten. Therefore, it would be advantageous to provide an open framework for the definition of metadata.
The present invention provides a family of Java interfaces that define methods to provide common information about a property, such as data type and editing capabilities. The interfaces identify the methods used to get generic metadata. Implementers may extend these interfaces, as needed, to provide the metadata for their specific properties. For example, when a relational database is added, a programmer may write an object descriptor and a property descriptor classes that extend the interfaces. The common metadata description interface of the present invention allows multiple metadata sources to be used interchangeably within the same software product without the software code being specifically written for each metadata source.
The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:
With reference now to the figures,
In the depicted example, a server 104 is connected to network 102 along with storage unit 106. In addition, clients 108, 110, and 112 also are connected to network 102. These clients 108, 110, and 112 may be, for example, personal computers or network computers. In the depicted example, server 104 provides data, such as boot files, operating system images, and applications to clients 108-112. Clients 108, 110, and 112 are clients to server 104. Network data processing system 100 may include additional servers, clients, and other devices not shown. In the depicted example, network data processing system 100 is the Internet with network 102 representing a worldwide collection of networks and gateways that use the TCP/IP suite of protocols to communicate with one another. At the heart of the Internet is a backbone of high-speed data communication lines between major nodes or host computers, consisting of thousands of commercial, government, educational and other computer systems that route data and messages. Of course, network data processing system 100 also may be implemented as a number of different types of networks, such as for example, an intranet, a local area network (LAN), or a wide area network (WAN).
In accordance with a preferred embodiment of the present invention, Java programs may be called from within HTML documents or launched stand alone within network data processing system 100. When a Java program runs on a client, such as clients 108, 110, 112, it is often called a “Java applet.” When it is run on a server, such as server 104, it is called a “servlet.”
The present invention provides a family of Java interfaces that define methods to provide common information about a property, such as data type and editing capabilities. Implementers may extend these classes as needed to provide the metadata for their specific properties. For example, one embodiment of the present invention is an implementation that provides metadata descriptions of columns in a database table could be realized using Java DataBase Connectivity. Another example may be an implementation that uses Java introspection to glean metadata information about any bean object. The common metadata description interface of the present invention allows these two implementations to be used interchangeably within the same software product.
Peripheral component interconnect (PCI) bus bridge 214 connected to I/O bus 212 provides an interface to PCI local bus 216. A number of modems may be connected to PCI bus 216. Typical PCI bus implementations will support four PCI expansion slots or add-in connectors. Communications links to network computers 108-112 in
Additional PCI bus bridges 222 and 224 provide interfaces for additional PCI buses 226 and 228, from which additional modems or network adapters may be supported. In this manner, data processing system 200 allows connections to multiple network computers. A memory-mapped graphics adapter 230 and hard disk 232 may also be connected to I/O bus 212 as depicted, either directly or indirectly.
Those of ordinary skill in the art will appreciate that the hardware depicted in
The data processing system depicted in
With reference now to
An operating system runs on processor 302 and is used to coordinate and provide control of various components within data processing system 300 in
Those of ordinary skill in the art will appreciate that the hardware in
As another example, data processing system 300 may be a stand-alone system configured to be bootable without relying on some type of network communication interface, whether or not data processing system 300 comprises some type of network communication interface. As a further example, data processing system 300 may be a Personal Digital Assistant (PDA) device, which is configured with ROM and/or flash ROM in order to provide nonvolatile memory for storing operating system files and/or user-generated data.
The depicted example in
With reference to
The interface IMetaPropertySetDescriptor 404 describes a set of properties, such as a group of columns in a database. The IMetaObjectDescriptor interface 406 extends IMetaPropertySetDescriptor to collect multiple associated property descriptions into a single object description. Interface 404 is a subclass of interface 406. The arrow between interface 402 and 404 represents association. The arrow indicates that an object that implements interface 404 has a one-way association with objects that implement interface 402. Besides inheritance and association, relationships may include aggregation, using, instantiation, and meta-class. The “1 . . . *” indicates the cardinality of the association; a property set is associated with one or more properties. This is a one-to-many association. Other cardinalities may include one-to-one or many-to-many.
The methods of the IMetaProperty Descriptor are as follows:
The methods of the IMetaPropertySetDescriptor interface are as follows:
The methods of the IMetaObjectDescriptor interface are as follows:
With reference now to
An ObjectDescriptor class 510 that implements the interface IMetaObjectDescriptor is created. For example, if an enterprise uses a relational database, a programmer may create an ObjectDescriptor specifically for the relational database. The ObjectDescriptor includes the actual code for the methods identified in interface 506 and may glean information about an object. Next, a PropertyDescriptor class 508 that implements interface IMetaPropertyDescriptor 502 is created to expose information about each property in the object. In other words, the PropertyDescriptor class includes the actual code for the methods that are identified in the IMetaPropertyDescriptor interface. These methods may be called to return metadata for a property. For example, for a relational database, each property may be represented by a column and the PropertyDescriptor may be written to provide the actual code for the methods identified in interface 502.
Interfaces 502, 504, 506 are universal. ObjectDescriptor and PropertyDescriptor classes are specific to a metadata source. An enterprise may create an OjbectDescriptor and one or more PropertyDescriptors when a metadata source is added. ObjectDescriptor and PropertyDescriptor classes may also be shared between enterprises. In fact, a developer of a data source, such as a database, may write an ObjectDescriptor and appropriate PropertyDescriptors to ship with the product. Once this framework is in place, software may be written as if all the programmer knows is that there is an object that has properties. This simplifies the programming significantly when multiple metadata sources are being used. Furthermore, software written for this open framework may be used even after new data sources are added.
A DBTableObjectDescriptor class 612 that implements the interface IMetaObjectDescriptor is created. The DBTableObjectDescriptor class may glean information about the appropriate database table using APIs that talk to the backend database and use the methods defined in interface IMetaObjectDescriptor 606 to expose that information. Next, a DBColumnPropertyDescriptor class 608 that implements the IMetaPropertyDescriptor interface 602 is created to expose information about each appropriate database table column (again using APIs that talk to the backend database) and use the methods defined in interface IMetaPropertyDescriptor 602 to expose that information.
Similarly, a JavaBeanObjectDescriptor class 614 that implements the interface IMetaObjectDescriptor is created. The JavaBeanObjectDescriptor class may glean information about the JavaBean using Java's built-in object introspection mechanism and use the methods defined in interface IMetaObjectDescriptor 606 to expose that information. Next, JavaBeanPropertyDescriptor class 610 that implements the IMetaPropertyDescriptor interface 602 is created to expose information about each property in the JavaBean using Java's built-in method introspection mechanism. Thus, the family of Java interfaces that make up the common interface may be implemented to expose information from multiple metadata sources, in this example one source being a relational database and the other being a Java Bean object.
An example Java program for a property sheet editor written using the open framework of the present invention follows:
Next, in line 1010, the program uses the methods in the framework to get the number of properties and loops through the properties. Line 1015 gets the property descriptor from the object descriptor. Line 1020 gets the property name and line 1025 gets the property value. Next, line 1030 gets a property editor from the property descriptor. (For a description of property editors see SUN Java Bean specification, Java Platform Second Edition, version 1.1 API.) This is used to populate a text field user interface widget with a textual representation of the property's value. In line 1035, this text field widget is associated with the property's name and is saved to a lookup table.
Thereafter, line 1050 defines a method called “save” that takes an ObjectDescriptor and an object as values. Next, in line 1055, the program uses the methods in the framework to get the number of properties and loops through the properties. Line 1060 gets the property descriptor from the object descriptor. Line 1065 gets the property name. Next, line 1070 extracts the textual representation of the edited property value from the text field widget that was previously saved to a lookup table and converts it to the property value object using the property editor. Line 1075 gets the property value object from the property editor. Thereafter, in line 1080, the property's new value is saved back into the containing object. This completes the editing process.
As can be seen in the above example, a program may be written without identifying an object type or a metadata source. The example property sheet program may be used for multiple data sources and may be reused in any environment taking advantage of the open framework of the present invention. While the example program is written in Java, other programming languages may be used, such as C++.
With reference now to
Thus, the present invention solves the disadvantages of the prior art by providing a family of Java interfaces that makes up a common interface for multiple metadata sources. Classes that implement these interfaces may extend these classes as needed to provide the metadata for their specific properties. Multiple implementations may be used interchangeably within an application because of the common metadata description provided by the interfaces. This technique is useful in cases in which properties are dynamically created at runtime and, therefore, cannot be described using a concrete bean object defined at compile time.
It is important to note that while the present invention has been described in the context of a fully functioning data processing system, those of ordinary skill in the art will appreciate that the processes of the present invention are capable of being distributed in the form of a computer readable medium of instructions and a variety of forms and that the present invention applies equally regardless of the particular type of signal bearing media actually used to carry out the distribution. Examples of computer readable media include recordable-type media, such as a floppy disk, a hard disk drive, a RAM, CD-ROMs, DVD-ROMs, and transmission-type media, such as digital and analog communications links, wired or wireless communications links using transmission forms, such as, for example, radio frequency and light wave transmissions. The computer readable media may take the form of coded formats that are decoded for actual use in a particular data processing system.
The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.