Gianfranco R. Putzolu

System R: relational approach to database management

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.

Granularity of locks in a shared data base

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.

System R: an architectural overview

We have described the architecture of System R, including the Relational Data System and the Research Storage System. The RDS supports a flexible spectrum of binding times, ranging from precompilation of “canned transactions” to on-line execution of ad hoc queries. The advantages of this approach may be summarized as follows: 1. For repetitive transactions, all the work of parsing, name binding, and access path selection is done once at precompilation time and need not be repeated. 2. Ad hoc queries are compiled on line into small machine-language routines that execute more efficiently than an interpreter. 3. Users are given a single language, SQL, for use in ad hoc queries as well as in writing PL/I and COBOL transaction programs. 4. The SQL parser, access path selection routines, and machine language code generator are used in common between query processing and precompilation of transaction programs. 5. When an index used by a transaction program is dropped, a new access path is automatically selected for the transaction without user intervention.

Probabilistic aspects of machine decomposition theory

Results obtained concern the likelihood that randomly chosen machines admit nontrivial decompositions of their state behavior.

Frequency of decomposability among machines with a large number of states

In a universe of machines with n labeled states and p labeled inputs, it is shown that almost all machines have series-parallel decomposition if n and p approach infinity in such a way that pn^1^/^2e^-^n->0. Also, almost all machines have no series-parallel decomposition if n and p approach infinity in such a way that pn^1^/^6e^-^n->~.