We develop new algorithms for the management of transactions in a page-shipping client-server database system in which the physical database is organized as a sparse B-tree index. Our starvation-free fine-grained locking protocol combines adaptive callbacks with key-range locking and guarantees repeatable-read-level isolation (i.e., serializability) for transactions containing any number of record insertions, record deletions, and key-range scans. Partial and total rollbacks of client transactions are performed by the client. Each structure modification such as a page split or merge is defined as an atomic action that affects only two levels of the B-tree and is logged using a single redo-only log record, so that the modification never needs to be undone during transaction rollback or restart recovery. The steal-and-no-force buffering policy is applied by the server when flushing updated pages onto disk and by the clients when shipping updated data pages to the server, while pages involved in a structure modification are forced to the server when the modification is finished. The server performs the restart recovery from client and system failures using an ARIES/CSA-based recovery protocol. Our algorithms avoid accessing stale data but allow a data page to be updated by one client transaction and read by many other client transactions simultaneously, and updates may migrate from a data page to another in structure modifications caused by other transactions while the updating transaction is still active.

No abstract

This paper presents initial results regarding writing activities in the context of the ALADDIN project. The goal of the project is to teach Modern Standard Arabic in 5-year-old kindergarten students in Qatar. A total of 18 students, enrolled in the 'Arabic Class', participated for 9 weeks in the activities of the project. All students were native speakers of the Qatari dialect. Learning activities involved both typical instructional methods, and the use of specifically designed tools for tabletop surface computers. The paper focuses on writing activities and on how the affordances of surface computers affected students' performance and attitude towards the Arabic class and, consequently, the Arabic language.

No abstract

No abstract