Arthur M. Keller’s research while affiliated with Mountain View College and other places

This paper discusses a framework for the design of a security component for a secure Ada data- base management system (DBMS). It is part of a de- velopment effort to produce prototype technologies for the World Wide Military Command and Control Sys- tem (WWMCCS) Information System (WIS). In this paper we present a series of criteria for evaluating data- base security approaches. We develop the high-level framework for the'security component of a DBMS and illustrate how it can support several alternative security models, which we compare using these criteria. The se- curity enforced by the DBMS relies an appropriate se- curity mechanisms enforced by the operating systems for operating system objects, such as files, used by the DBMS. We also present the security barrier or filter as an alternative or adjunct to the notion of a trusted computer base.

DIANA (Device-Independent, Asynchronous Network Access) is a new application architecture to solve two major difficulties in developing software for mobile computing—diversity of user interface and varied communication patterns. Our architecture achieves display and network independence by de-coupling the user interface logic and communication logic from the processing logic of each application. Such separation allows applications to operate in the workplace as well as in a mobile environment in which multiple display devices are used and communication can be synchronous or asynchronous. Operation during disconnection is also supported.

In this work we address the problem of dealing with data inconsistencies while integrating data sets derived from multiple autonomous relational databases. The fundamental assumption in the classical relational model is that data is consistent and hence no support is provided for dealing with inconsistent data. Due to this limitation of the classical relational model, the semantics for detecting, representing, and manipulating inconsistent data have to be explicitly encoded in the applications by the application developer.

Infomaster is an information integration system that provides integrated access to multiple distributed heterogeneous information sources on the Internet, thus giving the illusion of a centralized, homogeneous information system. We say that Infomaster creates a virtual data warehouse. The core of Infomaster is a facilitator that dynamically determines an efficient way to answer the user's query using as few sources as necessary and harmonizes the heterogeneities among these sources. Infomaster handles both structural and content translation to resolve differences between multiple data sources and the multiple applications for the collected data. Infomaster connects to a variety of databases using wrappers, such as for Z39.50, SQL databases through ODBC, EDI transactions, and other World Wide Web (WWW) sources. There are several WWW user interfaces to Infomaster, including forms based and textual. Infomaster also includes a programmatic interface and it can download results in structur...

this paper, we discuss the principles, architecture, and implementation of the Penguin approach to sharing persistent objects. The primary motivation for using a database management system (DBMS) is to allow sharing of data among multiple customers and multiple applications. To support sharing among independent transactions, DBMSs have evolved services including transaction independence, persistence, and concurrency control. When a database is shared among multiple applications, these applications typically have differing requirements for data access and representation. Such differences are supported by having views, which present diverse subsets of the base data [ChamGT75]. The primary motivation for defining objects is to include sharable semantics and structure in the information. Must all applications sharing objects use the same object schema, or is it better to give each application its own object schema and somehow to integrate them? If multiple applications differ in view the needed compromise reduces the relevance and effectiveness of the object representation [AbitB91]. For instance, customers will have an orthogonal view of an inventory versus the suppliers. 2 When combining independently developed applications, we do not have the luxury of choosing a common object schema. Many legacy databases and legacy data are still being used. We must retain the investment in existing application software and databases, while building new software using the object approach. When creating a federation of heterogeneous (pre-existing) databases, we must support a degree of interoperation among these databases and their schemas. Consider also that current projects will become legacy in a few years hence, but their semantics will remain. Whatever solutions we create in shar...

In this paper we present a classification of the methods for updating replicated databases. The main contribution of this paper is to present the various methods in the context of a structured taxonomy, which accommodates very heterogeneous methods. Classes of update methods are presented through their general properties, such as the invariants that hold for them. Methods are reviewed both in their normal and abnormal behaviour (i.e., after a network partition). We show that several methods presented in the literature, sometimes in independent papers with no crossreference, are indeed very much related, for instance because they share the same basic technique. We also show in what sense they diverge from the basic technique. This classification can serve as a basis for choosing the method that is most suitable to a specific application. It can also be used as a guideline to researchers who aim at developing new mechanisms. 1 Introduction One of the major obstacles to the dev...

We present the case for allowing independent updates on replicated databases. In autonomous, heterogeneous, or large scale systems, using two-phase commit for updates may be infeasible. Instead, we propose that a site may perform updates independently. Sites that are available can receive these updates immediately. But sites that are unavailable, or otherwise do not participate in the update transaction, receive these updates later through propagation, rather than preventing the execution of the update transaction until sufficient sites can participate. Two or more sites come to agreement using an reconciliation procedure that uses reception vectors to determine how much of the history log should be transferred from one site to another. We also consider what events can initiate a reconciliation procedure. 1 Introduction Many recent papers have studied the applicability of replicated databases, and many strategies have been developed to deal with updates in such an environment [1, 6, 7...

We have created a "dataweb" of financial services data for Merrill Lynch using Infomaster. Merrill Lynch has about 20 separate systems containing data on commercial customer accounts. There are many commercial customers with multiple relationships with Merrill Lynch and therefore have accounts represented in multiple systems. There is common data in multiple customer records across the different systems that can be used to link them. However, the common data is entered manually and does not have referential integrity across the systems. Merrill Lynch is creating the Cross-Reference Utility (CRU) to link the customer data together. CRU is used both for inquiries by account representatives and for cleaning up the incorrect cross-system references. Stanford's Center for Information Technology is experimenting with Infomaster as a "shadow" project to CRU. The primary differences between the CRU approach and the Infomaster approach are: (1) CRU assigns CRU IDs to each customer, so there is ...

This paper presents a detailed performance study of three associative caching schemes for client-server databases. In all the three schemes, the client cache loads query results dynamically in the course of transaction execution, and supports evaluation of associative queries on the cache, at the cost of refreshing the cached data and maintaining transaction serializability through asynchronous update notifications from the server. The schemes differ in the way they handle cache containment reasoning and data updates. In one scheme, the cache derives a description of its current contents from the stored queries, and uses predicate-based reasoning to examine and maintain the cache. The second scheme is an optimized version of the first, and considers partial containment of cached queries. It also performs writes at the central server in case of a cache miss. The third caching scheme operates in terms of tuples only, requiring trips to the server to determine cache containment of associa...

This paper presents a detailed performance study of the associative caching scheme proposed in [11]. A client cache dynamically loads query results in the course of transaction execution, and formulates a description of its current contents. Predicate-based reasoning is used on the cache description to examine and maintain the cache. The benefits of the scheme include local evaluation of associative queries, at the cost of maintaining the cached query results through update notifications from the server. In this paper, we investigate through detailed simulation the behavior of this caching scheme for a client-server database under different workloads and contention profiles. An optimized version of our basic caching scheme is also proposed and studied. We examine both read-only and update transactions, with the effect of updates on the caching performance as our primary focus. Using an extended version of a standard database benchmark, we identify scenarios where these caching schemes ...