Adaplex is an integrated language for programming database applications. It results from the embedding of the database sublanguage Daplex in the general-purpose programming language Ada [1]. This paper describes the design of DDM, a general-purpose distributed database management system implemented in Ada that supports the use of Adaplex as interface language. There are two novel aspects in the design of this system. First, this is the first full-scale distributed database system to support a semantically rich, functional data model. DDM goes beyond systems like Distributed INGRES and R*(which are based on the relational technology) in providing advanced data modeling capabilities and ease of use. Second, this is the first full-function distributed DBMS designed to be compatible with the Ada programming environment. The coupling between Ada and Daplex has been achieved at the expression level which is much tighter than the statement level integration attained in previous systems. This tight coupling poses new implementation problems but also creates new opportunities for optimization. The current paper highlights the Adaplex language and discusses innovative aspects in DDM's design that are intended to meet the dual objectives of good performance and high data availability.

We describe a reliability algorithm being considered for DDM, a distributed database system under development at Computer Corporation of America. The algorithm is designed to tolerate clean site failures in which sites simply stop running. The algorithm allows the system to reconfigure itself to run correctly as sites fail and recover. The algorithm solves the subproblems of atomic commit and replicated data handling in an integrated manner.

Adaplex is an integrated language for programming database applications. It results from the embedding of the database sublanguage DAPLEX in the general purpose programming language Ada. This paper provides an overview of the DDM: a distributed database manager (DDM) that supports the use of Adaplex as an interface language. The important technical innovations we have incorporated in the design of this system include:1. An advanced data model that captures more application semantics than conventional data models.2. Support for flexible data distribution options that improve locality of reference and efficiency of query processing.3. Extensive query optimization that combines compile time access path optimization with run time site selection.4. Efficient transaction management that reduces transaction conflicts and improves the resiliency of replicated data.5. Robust, incremental recovery management that provides for automatic recovery from certain "catastrophic" failure conditions.

This paper describes the implementation level design of an integrated concurrency control and recovery scheme based on the maintenance of multiple versions of data objects in a database. The concurrency control mechanism enhances parallelism by eliminating interference between retrieval and update transactions. The recovery mechanism permits efficient transaction and system recovery by keeping before-images of data objects at the page (block) level. This paper addresses the key technical problems in the implementation of such an integrated scheme. We present an efficient garbage collection algorithm for reclaiming storage space used by old versions of data objects that will no longer be accessed. We also propose an on-line backup algorithm that will permit the backup procedure to run in parallel with regular transactions. This integrated concurrency control and recovery scheme is being implemented in the LDM: the local database manager component of a distributed database management system, now being developed by Computer Corporation of America, that will support the ADAPLEX database application programming language [Chan81a, Smith81].

The declining cost of computer hardware and the increasing data processing needs of geographically dispersed organizations have led to substantial interest in distributed data management. SDD-1 is a distributed database management system currently being developed by Computer Corporation of America. Users interact with SDD-1 precisely as if it were a nondistributed database system because SDD-1 handles all issues arising from the distribution of data. These issues include distributed concurrency control, distributed query processing, resiliency to component failure, and distributed directory management. This paper presents an overview of the SDD-1 design and its solutions to the above problems. This paper is the first of a series of companion papers on SDD-1 (Bernstein and Shipman [2], Bernstein et al. [4], and Hammer and Shipman [14]).