All eqmvalence is estabhshed between network databases and a subclass of relational databases. A database is a set of files together w~th a set of constraints that the fdes must satisfy. The constraints are spectfied by Bachman diagrams m the network model and by data dependencies m the relational model. The subclass of relatmnal databases of interest ~s characterized by the absence of two properties of data dependencies: conflzct and contention It is proved that network databases with loop-free Bachman diagrams are eqmvalent to relational databases which are free of conflicts and contenUons. When its Bachman dmgram has loops, a network database ts equivalent to a collection of relattonal databases in this subclass.Th~s study of equivalence is also related to database design algorithms. Although the network model cannot capture the nouons of conflict and contention, they are the source of several problems which have been observed in the decomposiuon approach to relational database design, notably the split key problem, the nonumqueness problem, and lossy joins It is shown that the decomposition approach can be apphed to conflict-and contention-free relational databases without any of these problems.The results serve as a theorettcal foundatton for database translatton between different models and for designing multimodel database management systems.

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Most database design methods for the relational model produce a flat database, that is, a family of relations with no explicit interrelational connections. The user of a flat database is likely to be unaware of certain interrelational semantics. In contrast, the entity-relationship model provides schema graphs as a description of the database, as well as for navigating the database. Nevertheless, the user of an entity-relationship database may still commit semantic errors, such as performing a lossy join. This paper proposes a nonflat, or hierarchical, view of relational databases. Relations are grouped together to form relation hierarchies in which lossless joins are explicitly shown whereas lossy joins are excluded. Relation hierarchies resemble the schema graphs in the entity-relationship model.An approach to the design of relation hierarchies is outlined in the context of data dependencies and relational decomposition. The approach consists of two steps; each is described as an algorithm. Algorithm DEC decomposes a given universal relation according to a given set of data dependencies and produces a set of nondecomposable relation schemes. This algorithm differs from its predecessors in that it produces no redundant relation schemes. Algorithm RH further structures the relation schemes produced by Algorithm DEC into a hierarchical schema. These algorithms can be useful software tools for database designers.

When stricken by a catastrophic natural disaster, emergency rescue operation is very critical to many lives. Many people trapped in the disastrous areas under collapsed buildings or landslides may have a large chance to survive if they are rescued in "Golden 72 Hours". Victims rescued from the debris and evacuated from their home jammed in shelters need life support material to support their lives. They also need to communicate to each other for various reasons. However, communication systems were usually down due to various reasons. The loss of communication systems and information networks made the rescue and relief operation extremely difficult. Many people died before they got a chance to be rescued. This paper analyzes the causes that paralyzed the entire communication systems in Jiji/Taiwan Earthquake and proposes a MANET based communication platform as well as a Rescue Information System for Earthquake Disasters that can support a large number of rescue volunteers under catastrophic natural disasters.