The recovery subsystem of an experimental data management system is described and evaluated. The transactmn concept allows application programs to commit, abort, or partially undo their effects. The DO-UNDO-REDO protocol allows new recoverable types and operations to be added to the recovery system Apphcation programs can record data m the transaction log to facilitate application-specific recovery. Transaction undo and redo are based on records kept in a transaction log. The checkpoint mechanism is based on differential fries (shadows). The recovery log is recorded on disk rather than tape.

System R is a database management system which provides a high level relational data interface. The system provides a high level of data independence by isolating the end user as much as possible from underlying storage structures. The system permits definition of a variety of relational views on common underlying data. Data control features are provided, including authorization, integrity assertions, triggered transactions, a logging and recovery subsystem, and facilities for maintaining data consistency in a shared-update environment.This paper contains a description of the overall architecture and design of the system. At the present time the system is being implemented and the design evaluated. We emphasize that System R is a vehicle for research in database architecture, and is not planned as a product.

System R is a database management system which provides a high level relational data interface. The system provides a high level of data independence by isolating the end user as much as possible from underlying storage structures. The system permits definition of a variety of relational views on common underlying data. Data control features are provided, including authorization, integrity assertions, triggered transactions, a logging and recovery subsystem, and facilities for maintaining data consistency in a shared-update environment.This paper contains a description of the overall architecture and design of the system. At the present time the system is being implemented and the design evaluated. We emphasize that System R is a vehicle for research in database architecture, and is not planned as a product.

The Pilot operating system provides a single-user, single-language environment for higher level software on a powerful personal computer. Its features include virtual memory, a large "flat" file system, streams, network communication facilities, and concurrent programming support. Pilot thus provides rather more powerful facilities than are normally associated with personal computers. The exact facilities provided display interesting similarities to and differences from corresponding facilities provided in large multi-user systems. Pilot is implemented entirely in Mesa, a highlevel system programming language. The modularization of the implementation displays some interesting aspects in terms of both the static structure and dynamic interactions of the various components.

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