Chapter 1: Web-Hermes 1.0 Overview

• 1.1 -- Introduction:  The computer industry's rapid evolution soon spawned a plethora of diverse, often incompatible, hardware and software systems. This presents a major problem for today's businesses as cooperative efforts commonly requires data sharing. To address this, many companies developed, and adhere to, common communications protocols, such as CORBA or ODBC, for database systems -- They press data applications into a common mold. While such practice provides easy communications between like systems (mostly on like platforms), such standards often apply only to those systems similar and currently in existence (common to many users too) and frequently neglect large, non-public, legacy systems common in corporate, governmental and military establishments.

    The University of Maryland's Hermes project addresses these concerns by defining a language and software system which allows integration of like and non-like data sources through an adaptable software communications layer -- We modify the software to suit the data application. This allows easy communication between diverse data applications, distributed often across networks, and potentially implemented on a variety of hardware platforms. Simply stated, Hermes readily adapts to legacy and future software applications.
 
• 1.2 -- Hermes (HEterogeneous Reasoning and MEdiator System) specifics: The Hermes Project defines a unified theoretical framework and a set of practical software programs that provide an application-independent platform for scalable software and data integration across local and wide area networks. The Hermes software consists of adaptable search engine code and a variety of front-end user interfaces which mask the underlying complexity and convey an integrated data schema to the user.

    Sparc stations, Macintoshes, PC Laptops, and even the new Windows CE palm-top devices -- Global Hermes usage became possible with the Web-Hermes front-end development; Through dynamic Hermes HTML pages for the world-wide-web, users can access widely distributed Hermes search engines using common Web browsers available on many platforms.

    Hermes renders a logic-based database system which provides a simple, but powerful, framework for solving many problems described by C.J.Date in An Introduction to Database Systems, Volume I, Addison-Wesley, 1990, page 643.
 
• 1.2.1 -- Representational uniformity: It becomes possible to define a database language in which base data, "deductive axioms", queries, and integrity constraints are all represented in the same uniform way.
 
• 1.2.2 -- Operational uniformity: Proof theory provides a basis for a unified attack on a variety of apparently distinct problems, including query optimization (especially semantic optimization), integrity constraint enforcement, database design (dependency theory), program correctness proofs, and other problems.
 
• 1.2.3 -- Semantic modeling: Proof theory also provides a good basis on which to define various semantic modeling extensions, such as events, type hierarchies, and certain types of entity aggregation.
 
• 1.3 -- Hermes currently provides many of these capabilities, and others are being added; It extends the general logic-based approach in several directions, using concepts that are simple, general, and powerful.

• 1.3.1 -- Hermes extends its rules with functions that access external software and data. While a traditional rule-based system is limited to its own closed world or specialized domain, Hermes adds functions that open the system to the world and many domains. Commercial software currently integrated with Hermes includes relational databases (dBase and Paradox on the Windows platform). Public domain software includes University Ingres and two U.S. Army route planning packages on the UNIX systems. Other integrated software has been developed at the University of Maryland, including flat file relations, spatial databases, multimedia databases (including image, text and audio databases, plus face recognition software), and numerical software (linear programming). Hermes can also access the Internet to retrieve data, images, text and audio from around the world.

• 1.3.2 -- Hermes applies metalevel operators to elements of the logical language to extend the language power. Currently implemented operators can:
 
• intelligently cache functions and predicates;
• do repeated actions;
• save actions for a user to invoke; and
• print the set of answers for a query to a file for further processing.
 
• 1.3.3 -- Hermes provides client/server capabilities that allow queries to be distributed across a network, using different types of software on different machines and operating systems.
 
• 1.3.4 -- Hermes mediators contain sets of backward-chaining rules that can access, combine and mediate diverse software and data. The same logical language is used for defining rules as for querying mediators. Hermes rules apply predicates, comparisons, assignments and array, record and set operators to constants, variables and functions. The predicates are annotated with numeric truth values that state their relative confidence or certainty, as in traditional expert systems.
 
• 1.3.5 -- Hermes domains allow software and data abstractions that may be viewed from a logical perspective separate from the underlying implementation. Such abstractions range from large programs, such as a relational database management system, to sets of related functions, such as mathematics functions, tapped from the host operating system.
 
    Each domain contains one or more functions. A domain function is a high-level function that accesses software and data in a domain. A domain function is declared with its inputs and output and a brief English description of its process. At the programming interface level, a domain function may be implemented with calls to external programs (such as a relational database management system), C calls to other modules linked with Hermes (such as a text database), or a block of C code (such as for mathematical functions). Hermes provides the flexibility to integrate only the necessary functions from a software program; new functions can be added any time. The Hermes language provides a simple and uniform logical framework for solving many problems and for rapidly developing new applications.
 
• 1.3.6 -- The distributed version of Hermes utilizes query servers and domain function servers to access software and data across a network. For distributing queries across the Internet, Hermes basically uses a few network communication functions on top of some of the Hermes modules. This approach efficiently provides a general-purpose distributed implementation that is intelligent, flexible and scalable. Domain function servers provide a simple and general method of distributing queries across the Internet and other networks. These servers combine some of the Hermes modules with the domain interfaces for the software that is used on a given machine. (The application software may in turn access data distributed on various machines.) The domain function servers provide a general and uniform means to access software and data on remote machines, and can easily be configured to provide exactly the necessary domain functions on a given machine. The TCP/IP stream socket communications between a mediator and any domain function servers that it accesses are automated by Hermes. The same domain interface code can be used on a local machine as on a remote machine -- it is only necessary to use a few predefined functions in the interface to direct the domain function to a remote machine if necessary. The character-based communications protocol facilitates portability across different types of machines and networks. The results of remote domain functions can be stored on a local machine and reused as appropriate. Hermes currently runs across the Internet and can easily be scaled up to include many sites.
 
• 1.4 -- Technical challenges in implementing Hermes involve integrating software, integrating data, and distributing that software and data on a network. The problem of building integrated information systems is divided into two parts -- software integration and data integration. Software integration requires interfacing Hermes with the necessary functions provided by existing software. A domain catalog provides the mediator-level declarations of the domains and their functions. Once the necessary software functions have been integrated with Hermes, they can generally be used for a wide variety of applications without further interface programming. Once a software program has been integrated with Hermes, any database accessed by that program can be used in a mediator simply by declaring its location and type structure and by writing the appropriate rules. For integrating software, a domain function can be implemented with a fragment of C code (such as for mathematical functions), C calls to other modules linked with Hermes (such as to search a text database), or calls to separate programs (such as a relational database management system). Data integration requires defining the syntax and semantics of the data returned by the software functions. Data syntax is specified by data declarations in a mediator. Data declarations in a mediator describe the location and structure of the databases accessed by that mediator. Data semantics are specified by rules, which can access data, combine data and resolve conflicts. The Hermes standard data format for exchanging information with domains provides a rich set of data structures: single constants, records, arrays and sets -- in any combination. The Hermes language provides easy access to the elements of these data structures. Unstructured or binary data are exchanged through files.
 
• 1.4.1 -- Hermes provides a general-purpose logic-based graphical interface that uses the logical query language directly. Hermes also provides for application-specific graphical interfaces that can present the user with menus, lists and so forth. Both types of interface provide for multimedia answers, in the form of images, text and audio.
 
General goals of Hermes include:
 
• maximizing the variety of software and data that can be integrated;
• maximizing the interoperability between different software and data;
• minimizing the time to integrate new software and data; and
• minimizing the time to process queries to these integrated sources.
 
• 1.4.2 -- Hermes provides logical foundations, as well as a search engine and software tools and methodologies, to support these goals.

 
• 1.4.3 -- Hermes is implemented in C ; Standalone versions run both on Unix and (experimentally) on Microsoft Windows operating systems. The distributed version runs on Unix across the Internet, using TCP/IP stream sockets for the client/server communications.
 

• 1.5 -- Acknowledgments: Web-Hermes 1.0 is, and continues to be, a group effort; From the programmers poking through peculiar bits and bytes, to the theorists pondering distant goals, many (too many to cite) imaginative individuals have toiled long, sometimes difficult, hours to bring Web-Hermes into reality.

    Documentation has long been a problem as the Hermes target never ceases to change; Building on previous efforts, this document draws structure and basic background information from earlier notes written by Ross Emery, one of the founding project programmers. New sections include those (finally) defining procedures for software installation and compilation, guidance for writing mediators, and instructions for integrating future domains.
 
• 1.6 -- Audience: This manual is written for persons:
 
• using mediators, either interactively or from another program
• writing mediators
• integrating domains

    As such, it assumes some basic knowledge of logic programming and/or C programming, although there are many explanations and examples. Chapter 3 provides an overview of the current system architecture and the basic tasks associated with using the system. It also suggests which subsequent chapters would be helpful for performing which tasks.

    Some familiarity with logic programming is helpful in understanding Hermes and this guide, but Chapter 4 will provide a detailed explanation of the proof process for a simple example.

    Applications developed using Hermes typically have their own graphical interfaces which are separate from the Hermes logical language and easier to use. These interfaces would either be self-explanatory or have their own documentation.

    At the GUI level are easy-to-use application-specific graphical interfaces, which use menus, lists, fill-in-the-blanks, and so forth, rather than the Hermes logical language. More exotic multimedia interfaces are possible. For example, a travel planning application could let a user specify areas of interest by clicking on a map. The graphical interfaces for these applications would typically not require any knowledge of logic and would have their own documentation or be self-explanatory.
 

• 1.7 -- Font Conventions: Sample code and examples appear in figure boxes throughout the document. Actual program text appears in a Courier (sans-serif) fonts with appropriate comments in Times New Roman (serif).
 
• 1.8 -- Hermes language syntax is defined using BNF (Backus-Naur Form) notation, plus English description where the left side of a definition contains the term being defined. The right side contains one or more sub-terms, which have their own definitions, or text characters typed by the user.

 

 

• 1.9 -- World-wide web page: The Hermes research group's web home-page provides access to many Hermes and related research materials.

Web Accessibility