Patent Application
20050102277
Embodiments of the invention generally relate to the field of data dictionaries and, more particularly, to a system and method for a data dictionary cache in a distributed system.
Data access layer 120 provides a persistent data store for conventional distributed system 100. Data access layer 120 includes computing device 140, data source 150, and data dictionary 160. Computing device 140 may a general purpose computing device or a specialized database computing device. Computing device 140 includes a Database Management System (DBMS) to control the data in data source 150 including the overall organization of the data, retrieval of the data, and integrity of the data.
Data dictionary 160 provides a source of information in which the system data for distributed system 100 is defined in a logical way. System information includes information whose function is to define the semantic and syntactic properties of operational data, such as the type, length, and relationships of operational data. System information that is defined in data dictionary 160 is, generally, available to applications operating on user terminals 114-116. For example, applications operating on user terminals 114-116 may use data or variables that are defined in data dictionary 160. Thus, any change to the data and/or variables defined in data dictionary 160 may automatically affect the applications operating on user terminals 114-116. In addition, services sitting on top of the data dictionary use the defined types and values.
Distributed systems are increasingly using an application layer between user layer 110 and data access layer 120. To provide services to user layer 110, an application layer needs access to the information stored in the data dictionary. Also, distributed systems having an application layer may also have more than one database system in the data access layer. Thus, an application layer may need access to the information stored in multiple database systems of a data access layer.
Embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar elements.
Embodiments of the invention are generally directed to a system and method for a data dictionary cache in a distributed system. In an embodiment, software operating on an application server receives a request for system information (e.g., a data type). The application server may reference a data dictionary cache to obtain the requested system information. As further described below, in one embodiment, the application server may select one of a plurality of data dictionary caches to provide the requested system information.
User layer 210 is the interface between distributed system 200 and one or more users. The illustrated embodiment of user layer 210 includes user terminals 214-219. One or more of user terminals 214-219 may collect user input and send it to application layer 220 over network connection 225. Network connection 225 may be a wired or wireless connection to a Local Area Network (LAN), a Wide Area Network (WAN), a Metropolitan Area Network (MAN), and/or the Internet. User terminals 214-219 may be personal computers, notebook computers, personal digital assistants, telephones, and the like. In an embodiment in which network connection 225 connects to the Internet, one or more of user terminals 214-219 may have a Web browser to interface with the Internet.
Application layer 220 includes application servers 222-224. An application server broadly refers to a computing device that performs data processing. In a three-tier client/server environment, such as distributed system 200, application servers 222-224 may provide the business logic for distributed system 200. In an embodiment, application layer 220 includes a computing device (e.g., called a dispatcher) to perform load balancing among application servers 222-224. In an embodiment in which application layer 220 exchanges information with user layer 210 via the Internet, one or more of application servers 222-224 may be described as a Web application server. Application servers 222-224 may be implemented according to any of the Java 2 Enterprise Edition Specifications, for example, v1.4, published on Jul. 12, 2002 (hereinafter the J2EE Standard). The term J2EE application server broadly refers to an application server that implements, at least in part, one of the J2EE specifications.
The term database system refers to the combination of hardware and software that provides a persistent data store. Database system 310 includes data dictionary 360, computing device 333, and data source 235. Database system 320 similarly includes data dictionary 370, computing device 334, and data source 236. Computing devices 333 and 334 may include a general computing device or a specialized computing device. In an embodiment, computing devices 333 and/or 334 also include logic, for example, to provide a database management system.
In an embodiment, data dictionary 360 may provide system information for some of the applications (e.g., Customer Relationship Management (CRM) applications) operating on application servers 222-224. Similarly, data dictionary 370 may provide system information for a different set of applications (e.g., Human Resources (HR) applications) operating on application servers 222-224. The system information provided by data dictionaries 360 and 370 may include the structure of data types and the relationships between data types used in distributed system 300. Data dictionary 380 illustrates that, in an embodiment, one or more data dictionaries may be on an application server (e.g., application server 224 in application layer 220). In such an embodiment, one or more data dictionary caches may cache system information provided by data dictionary 380.
A data type defines, for example, how data is stored in memory. Different data types may exist because data may be used differently in distributed system 300. For example, character-type data is typically used to store and display values, whereas numerical-type data is used to perform calculations. Examples of data types used in distributed system 300 are further described below with reference to
Data dictionary caches 330 and 340 buffer at least a portion of a data dictionary. In an embodiment, data dictionary caches 330 and 340 buffer at least a portion of data dictionaries 360 and 370, respectively. In an alternative embodiment, data dictionary cache 330 buffers system information (e.g., data types and related services) for a first application (or set of applications, e.g., CRM applications) and data dictionary cache 340 buffers system information for a second application (or set of applications, e.g., HR applications). The term “cache” refers to memory (or a region of memory) whose function is to store information that is likely to be used again. A data dictionary cache refers to memory (or a region of memory) in an application server that stores information from an associated data dictionary. Data dictionary caches 330 and 340 may be volatile memory, non-volatile memory, or a combination thereof. Further examples of memory suitable for a data dictionary cache are further described below with reference to
In an embodiment, data dictionary broker agent (DD broker agent) 350 provides an interface between data dictionaries 360 and 370 and application server 222. DD broker agent 350 may receive, for example, requests for a data type from an application and determine whether the requested data type is available in data dictionary cache 330 and/or data dictionary cache 340. If the requested data type is not currently stored in one of data dictionary caches 330 or 340, DD broker agent 350 may access either data dictionary 360 or data dictionary 370 to obtain the requested data type. DD broker agent 350 is further discussed below with reference to
Complex type 520 refers to data types that hold multiple data items. In an embodiment, complex type 520 includes structure data type 530, list data type 540, and/or tree data type 550. In an embodiment, structure data type 530 contains one or more named fields. Each of the two or more named fields may contain a data type of any type. In an embodiment, flat structure data type 560 refers to a structured data type in which all of the named fields are scalar data types. List data type 540 refers to an ordered group of elements belonging to the same data type. In an embodiment, tree data type 550 refers to a data type having one root element and zero or more non-root elements. Each non-root element may have one predecessor element and zero, one, or more successor elements.
Data types may be defined independently of the applications that use them. Applications may use data types to define data objects. The term “data object” refers to a self-contained module of data and its associated processing. In an embodiment, data objects comply with the Java Specification Request 12 entitled, “Java Data Objects (JDO) Specification,” Apr. 30, 2002.
The illustrated embodiment of data dictionary cache service 620 includes data dictionary broker agent 630, data dictionary caches 640, 650, and 660, and data dictionary cache provider factory 670. Data dictionary (DD) broker agent 630 receives the request for a data type from application 610 and determines whether one (or more) of data dictionary caches 640, 650, and 660 contain the requested data type. In an embodiment, DD broker agent 630 implements a cache management policy for data dictionary caches 640, 650, and 660. The term “cache management policy” broadly refers to logic that performs the operations related to reading, storing, and maintaining information in a cache. In an embodiment, an implementation of a cache management policy dictates how DD broker agent 630 determines whether data dictionary caches 640, 650, and 660 contain the requested data type.
In an embodiment, if data dictionary caches 640, 650, and 660 do not contain the requested data type, then DD broker agent 630 obtains the requested data type from a data dictionary in data access layer 680. In an embodiment, DD broker agent 630 places the data type obtained from the underlying data dictionary into one of data dictionary caches 640, 650, and 660. Alternatively, DD broker agent 630 may use data dictionary cache provider factory 670 to generate a new data dictionary cache to store the obtained data type. Provider factory 670 is an object of the factory class as specified in the J2EE Standard. In an embodiment, provider factory 670 creates data dictionary caches according to the cache management policy implemented by data dictionary broker 630.
Turning now to
Referring to process block 720, one of a plurality of data dictionary caches is selected to provide the requested data type. In an embodiment, selecting an appropriate data dictionary cache is regulated by a cache management policy implemented by the DD broker agent. In an embodiment, each data dictionary cache corresponds to a specific data dictionary in a data access layer. In an alternative embodiment, each data dictionary cache corresponds to a particular component of the business logic operating in a distributed system (e.g., CRM applications or HR applications).
The DD broker agent determines whether the requested data type is stored in the selected data dictionary cache at reference numeral 730. In an embodiment, the cache management policy implemented by the DD broker agent specifies how the DD broker agent searches the selected data dictionary cache. If the selected data dictionary cache does not contain the requested data type, the DD broker agent obtains the requested data type from an underlying data dictionary at 740. In an embodiment there is one associated data dictionary for each data dictionary cache.
Referring to process block 750, a new data dictionary cache is created to store the obtained data type. In an embodiment, an instance of a data dictionary cache provider factory (e.g., provider factory 670 shown in
Data dictionary cache agent 850 enables node 800 to provide an interface between a data dictionary (or data dictionaries) and an application (or applications) seeking data types and related services from the data dictionary. Data dictionary cache agent 850 may be executable content, control logic (e.g., ASIC, PLD, FPGA, etc.), firmware, or some combination thereof, in an embodiment of the invention. In embodiments of the invention in which data dictionary cache agent 750 is executable content, it may be stored in memory 820 and executed by processor(s) 810.
Data dictionary caches 860 and 870 improve access to the system information in underlying data dictionaries by storing frequently (and/or recently) requested system information (and/or other metadata) in the application layer of a distributed system. In an embodiment, data dictionary caches 860 and 870 may be implemented as objects in volatile memory in compliance with, for example, the J2EE Standard. In alternative embodiments, data dictionary caches 860 and 870 may implemented according to different specifications and/or may be created in non-volatile memory.
Memory 820 may encompass a wide variety of memory devices including read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), random access memory (RAM), non-volatile random access memory (NVRAM), cache memory, flash memory, and other memory devices. Memory 820 may also include one or more hard disks, floppy disks, ZIP disks, compact disks (e.g., CD-ROM), digital versatile/video disks (DVD), magnetic random access memory (MRAM) devices, and other system-readable media that store instructions and/or data. Memory 820 may store program modules such as routines, programs, objects, images, data structures, program data, and other program modules that perform particular tasks or implement particular abstract data types that facilitate system use.
One or more I/O devices 830 may include a hard disk drive interface, a magnetic disk drive interface, an optical drive interface, a parallel port, serial controller or super I/O controller, serial port, universal serial bus (USB) port, a display device interface (e.g., video adapter), a network interface card (NIC), a sound card, modem, and the like. System interconnection 880 permits communication between the various elements of node 800. System interconnection 880 may include a wide variety of signal lines including one or more of a memory bus, peripheral bus, local bus, host bus, bridge, optical, electrical, acoustical, and other propagated signal lines.
It should be appreciated that reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Therefore, it is emphasized and should be appreciated that two or more references to “an embodiment” or “one embodiment” or “an alternative embodiment” in various portions of this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined as suitable in one or more embodiments of the invention.
Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.
