Manual Relational Databases: State of the Art Report 14:5

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Relational Databases explores the major advances in relational databases and provides a balanced analysis of the state of the art in relational.
Table of contents

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Classes table 60 also stores facet information in facet column In addition to these three tables 30 , 50 , and 60 , each database preferably also contains auxiliary tables that store user membership in groups and group permissions for reading and writing to different knowledge bases. Finally, Sophia contains an additional security database that handles user-group management, ontology permissions for individuals, session logging, and permission codes. For example, the permission code in permission column 44 of frames table 30 is associated with a definition in the security database: such definitions include a particular user or group, or the world.

Sophia may be implemented within a distributed computer system using any desired architecture; a preferred embodiment of an architecture is shown schematically in FIG. A knowledge base 76 is stored on a relational database server computer 80 which is accessed by a client computer 82 through a Web server Typically, Sophia is used as knowledge base storage for a particular system, such as RiboWeb, which contains additional components also located on Web server 70 or on a different Web server not shown.

A user at client computer 82 communicates with Sophia according to a particular knowledge base protocol and may have no knowledge of the underlying implementation of Sophia, beyond its support of the frame-based knowledge model. The user at client computer 82 uses a Web browser to access the system. Client computer 82 sends a query 72 , in a first format, for a subset 74 of frames contained within knowledge base 76 to Web server 70 e. After receiving query 72 , Web server 70 transfers it to the Sophia program 84 , which is preferably written in a scripting language, such as VBScript, JavaScript, or Perl.

These scripts 84 perform a variety of functions.

Conference proceedings and presentations

Scripts 84 translate query 72 into query 78 in a second or relational database format, preferably Structured Query Language SQL. Query 78 is then applied to select data from knowledge base 76 stored on server Any one or all of tables 30 , 50 , and 60 may be accessed during performance of the SQL query Execution of the SQL queries is performed in conjunction with a compatible database connection protocol of choice for connection with server The results of query 78 , subset 74 , are then returned to scripts It allows users to interact with Sophia without having any knowledge of the underlying table structure.

Subset 74 is preferably processed before being transmitted to client computer 82 as formatted output The same scripting language as executed the queries performs the processing. Such processing may include simple or more complex formatting according to the specifications of the user, or may regulate the security of the transaction. Access permissions associated with each frame or value in subset 74 are compared with a client identifier of client computer If client 82 does not have permission to access any data from subset 74 , such data will be removed from formatted output This function may also be performed as part of the SQL query.

Frames within subset 74 may also be tested to ensure that they are current according to a predetermined standard. Formatted output 84 may be in any format suitable for client computer For example, if client computer 82 accesses knowledge base 76 using a Web browser, formatted output 84 may be an HTML document.

Other functions performed by the scripts include application-state tracking and simple inference. That is, the system can infer that an instance of a class is also an instance of a superclass, even though the superclass is not directly associated with the instance in the tables. It can also infer that an instance inherits values from a class or superclass. Simple inference is enabled because this information, while not directly stored with the instance, is stored with a class or superclass and is therefore easily obtained.

Alternate embodiments of an architecture for implementing Sophia are shown in FIG. Scripts 84 and server 80 are identical to those of FIG. Although browsers are useful for human users, Sophia can also be accessed programmatically through its query applications programming interface API. With the API, Sophia can be used as a remote knowledge server.

For example, client 86 running Java and client 88 running Perl may both access Sophia through appropriate servers: Java server 90 and Perl server 92 , respectively. Any other types of connections with Sophia may be implemented. In FIGS. It is often useful to use a distributed network connection between server 80 and scripts However, Web server 70 , scripts 84 , and knowledge base 76 may all be stored on a single computer. The ODBC or other suitable connection between scripts 84 and server 80 allow both read and write operations.

That is, adding or editing frames in knowledge base 76 and retrieving frames from knowledge base 76 are performed according to the same protocol and by the same scripts When data is added, client 86 sends a query 72 in a first format to create a new frame. Scripts 84 translate the query into the second format 78 , which contains parameters e. A new record is then added to tables 30 , 50 , and 60 stored on database server An essential feature of Sophia is that it may be compatible with Open Knowledge Base Connectivity OKBC , a protocol for accessing knowledge bases stored in knowledge representation systems.

Thus, client applications may be written to access Sophia without relying on the details of the knowledge base implementation. OKBC is the emerging standard for knowledge base queries, and thus it is difficult to ensure full compatibility at any given time. Chaudhri et al. OKBC provides a set of operations for a generic interface to underlying knowledge representation systems, allowing for development of browsers and editors that may be implemented in a variety of programming languages, including Java, C, and Lisp.

Systems that are compatible with OKBC, as is Sophia, allow the specification and retrieval of data models using the OKBC core functions, and thus present a uniform interface, despite the detailed differences of the underlying implementation. OKBC allows data models to be updated dynamically, and also allows new relationships to be established between elements of the data model. OKBC queries, which can be considered to be in a knowledge base format, are implemented in Sophia by translating the queries into a relational database format, preferably SQL. Frame names collect information for most queries, and restrictions on slot and value cull the data.

The three main tables of FIGS. The scripting language may need to perform some data manipulation or simple computations in order to link the individual SQL queries together so as to obtain the desired output. Any required frame-based queries may be supported by Sophia. A relational database programmer of average skill will be able to translate any required query into SQL or other suitable database language given the details of the underlying table structure as explained above.

The following examples are included for illustration purposes. Two examples of OKBC queries are get-class-instances, which retrieves all instances of a particular class, including direct children and descendents related by subclass relationships; and get-class-subclasses, which retrieves all direct subclasses of a particular class. In SQL written to take advantage of Sophia's particular underlying data structure, these queries look as follows:.

Functions that are not explicit OKBC commands can also be created, such as delete-frames-by-session, which takes as input a user name and session ID and deletes records the user created during that session. As a further example, OKBC also allows users to insert values into frames and modify values with functions, such as put-slot-value to update a frame's slot value.

In the implementation of Sophia, this command is written as follows:. As explained with reference to FIGS. Similar interfaces have been used with prior art frame-based knowledge representation systems. The type of interface dictates the formatting performed by scripts 84 in order to produce formatted output Client applications interacting with Sophia through the query API may specify a suitable format for formatted output. The primary interface with Sophia is a Web browser located on client computer In selection pane , the user selects the browse or edit mode in field and the particular ontology from a drop-down list of ontology field Each ontology is stored in a separate database file.

Depending on the user's access permission, the user may edit account information, instances of classes create, delete, edit, rename, change permission , class hierarchy, and class relations. Preferably, class hierarchy and relations are altered only by system administrators and other privileged users.

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Sophia also preferably has a means for checking consistency and constraint enforcement of each change to the database performed in edit mode. The user can also navigate the class hierarchy Berthou, Tliste v. The user may open and close different branches of hierarchy as desired. Hierarchy is constructed using superclass-set table 50 of FIG. Query pane may be used to enter a query for a subset of frames in the knowledge base. Output pane displays output in a variety of forms.

As shown in FIG. The user may have obtained this pane by clicking on Publication in selection pane As a result, a query is executed to select all instances of the class Publication, which are displayed in output panel not shown. Such displayed instances are hyperlinked, so that clicking each instance causes a query to be executed to select the instance frame and its associated slots and values, leading to the display shown in FIG. Depending on the type of query performed, output pane displays output in a suitable format, including tables, as necessary.

In selection pane , the various options for adding or editing frames or user information are displayed. The edit panel displays the slots and values to be edited. A similar mechanism adds or edits all frames, except for instances, which are created using template slots provided from classes table 60 of FIG. When frames are added or edited, scripts 84 of FIG. Generation of HTML forms in which data are entered is known in the art.

It will be clear to one skilled in the art that the above embodiment may be altered in many ways without departing from the scope of the invention. For example, the particular languages OKBC and SQL are current standards for querying knowledge bases and relational databases, respectively. However, as such standards change name or form, the present invention can be adapted to accommodate such changes easily. Such straightforward variations are therefore well within the scope of the present invention.

Accordingly, the scope of the invention should be determined by the following claims and their legal equivalents. Effective date : A frame-based knowledge representation system is built on a relational database that is completely transparent to the user. A user at a client machine sends standard knowledge base queries across a distributed computer system and the system translates the queries into a language suitable for querying the database, such as Structured Query Language SQL.

The system stores a hierarchical data model that includes classes, particular instances of the classes, and relations among the classes and instances. Primitive objects, such as classes and instances, are organized with their associated attributes into frames. The system consists of three main tables and auxiliary tables.

The frames table stores frames with associated slots and values, along with associated ownerships, access permissions, and other facets. The superclass-set table stores the frames and associated superclasses or ancestor classes. The third table, the classes table, stores class frames, slots, and values, and a slot type designating a slot as own or template. The database also includes tables for security definitions, logging, and other features. To query the knowledge base, the user submits a query, preferably according to the Open Knowledge Base Connectivity protocol, and the system translates the query into SQL.

The result is formatted and processed to check user permissions before being returned to the user over the computer network. The system is accessed through a variety of interfaces, including a Web browser and various application programming interfaces. SUMMARY These objects and advantages are attained by a frame-based representation system built on a relational database that is hidden from the user. Instances occur at the leaves of the hierarchy and are used to store specific data.