How can an author store digital information so that it will be reliably intelligible, even years later when he or she is no longer available to answer questions? Methods that might work are not good enough; what is preserved today should be reliably intelligible whenever someone wants it. Prior proposals fail because they generally confound saved data with irrelevant details of today's information technology---details that are difficult to define, extract, and save completely and accurately.We use a virtual machine to represent and eventually to render any data whatsoever. We focus on a case of intermediate difficulty---an executable procedure---and identify a variant for every other data type.This solution might be more elaborate than needed to render some text, image, audio, or video data. Simple data can be preserved as representations using well-known standards. We sketch practical methods for files ranging from simple structures to those containing computer programs, treating simple cases here and deferring complex cases for future work. Enough of the complete solution is known to enable practical aggressive preservation programs today.

We describe a prototype system for reading IATA flight coupons. The system exploits various characteristics of IATA coupons to determine reliably coupon types and field boundaries, and to minimize the amount of manual keying. In particular, we propose a method for extracting and recognizing fixed-pitch characters on noisy images with a complex background. The method does not require a complete drop-out of background, pre-printed text, or lines before recognition, and allows for recovering partially damaged characters (e.g., overlap with form content, handwritten annotations, etc.).

OCR technology cannot on its own, meet the demands of automated data entry. Two types of postprocessing are generally required. First, context must be used to improve the recognition and accept some fields automatically. Second, operator intervention is needed to verify some results or enter fields that are too difficult to recognize. In this paper we describe a novel approach to integrate both types of post-processing into a single system. Context analysis and the interactive functions are invoked alternatively several times as needed. Each step improves the results until all fields are certified. The paper also discusses a framework for evaluating the efficiency of the method and provides some experimental results.

We present efficient and flexible methods which permit read-only transactions that do not mind reading a possibly slightly old, but still consistent, version of the data base to execute without acquiring locks. This approach avoids the undesirable interferences between such queries and the typically shorter update transactions that cause unnecessary and costly delays. Indexed access by such queries is also supported, unlike by the earlier methods. Old versions of records are maintained only in a transient fashion. Our methods are characterized by their flexibility (number of versions maintained and the timing of version switches, supporting partial rollbacks, and different recovery and buffering methods) and their efficiency (logging, garbage collection, version selection, and incremental, record-level versioning). Distributed data base environments are also supported, including commit protocols with the read-only optimization. We also describe efficient methods for garbage collecting unneeded older versions.

In engineering applications, multiple copies of object descriptions have to coexist in a single database. A scheme is proposed that enables users to explicitly deal with these object versions. After introducing a basic version model, the problem of rerouting interobject references on the creation of new versions is solved by providing generic references and user-specific environments. Logical version clusters are introduced that allow for the meaningful grouping of versions. Some remarks on implementation and a comparison with other approaches are also included.>

Relational database systems are attracting great interest from potential users outside the traditional areas in which such systems have been employed. Features of modern relational systems such as powerful query facilities, data and device independence, concurrency control, and recovery are useful in applications such as engineering design, office automation, and graphics. However, such applications place demands on the system that it must be extended to handle. This paper identifies three of these demands: storing non-coded information of arbitrary length within the database, dealing with aggregate objects as a unit, and improving support for interactive access. Additions to System R, a prototypical relational system, are introduced to satisfy these demands: long fields, for storing non-coded data, and complex objects, which declare the semantic relationships among data items and provide a means for adequately supporting interactive access.

System R supports a high-level relational user language called SQL which may be used by ad hoc users at terminals or as an embedded data sublanguage in PL/I or COBOL. Host-language programs with embedded SQL statements are processed by the System R precompiler which replaces the SQL statements by calls to a machine-language access module. The precompilation approach removes much of the work of parsing, name binding, and access path selection from the path of a running program, enabling highly efficient support for repetitive transactions. Ad hoc queries are processed by a similar approach of name binding and access path selection which takes place on-line when the query is specified. By providing a flexible spectrum of binding times, System R permits transaction-oriented programs and ad hoc query users to share a database without loss of efficiency. System R is an experimental database management system designed and built by members of the IBM San Jose Research Laboratory as part of a research program on the relational model of data. This paper describes the architecture of System R, and gives some preliminary measurements of system performance in both the ad hoc query and the “canned program” environments.

In a high level query and data manipulation language such as SQL, requests are stated non-procedurally, without reference to access paths. This paper describes how System R chooses access paths for both simple (single relation) and complex queries (such as joins), given a user specification of desired data as a boolean expression of predicates. System R is an experimental database management system developed to carry out research on the relational model of data. System R was designed and built by members of the IBM San Jose Research Laboratory.

A database system can generally be divided into three major components. One component supports the logical database as seen by the user. Another component maps the information into physical records. The third component, called the storage component, is responsible for mapping these records onto auxiliary storage (generally disks) and controlling their transfer to and from main storage. This paper is primarily concerned with the implementation of a storage component. It considers a simple and classical interface to the storage component: Seen at this level the database is a collection of segments. Each segment is a linear address space. A recovery scheme is first proposed for system failure (hardware or software error which causes the contents of main storage to be lost). It is based on maintaining a dual mapping between pages and their location on disk. One mapping represents the current state of a segment being modified; the other represents a previous backup state. At any time the backup state can be replaced by the current state without any data merging. Procedures for segment modification, save, and restore are analyzed. Another section proposes a facility for protection against damage to the auxiliary storage itself. It is shown how such protection can be obtained by copying on a tape (checkpoint) only those pages that have been modified since the last checkpoint.

System R is a database management system which provides a high level relational data interface. The systems 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.

This paper proposes a locking protocol which associates locks with sets of resources. This protocol allows simultaneous locking at various granularities by different transactions. It is based on the introduction of additional lock modes besides the conventional share mode and exclusive mode. The protocol is generalized from simple hierarchies of locks to directed acyclic graphs of locks and to dynamic graphs of locks. The issues of scheduling and granting conflicting requests for the same resource are then discussed. Lastly, these ideas are compared with the lock mechanisms provided by existing data management systems.