A Formal Characterization of Epsilon Serializability

Epsilon Serializability (ESR) is a generalization of classic serializability (SR). In this paper, we provide a precise characterization of ESR when queries that may view inconsistent data run concurrently with consistent update transactions. Our rst goal is to understand the behavior of queries in the presence of con icts and to show how ESR in fact is a generalization of SR. So, using the ACTA framework, we formally express the inter-transaction con icts that are recognized by ESR and through that de ne ESR, analogous to the manner in which con ict-based serializability is de ned. Secondly, expressions are derived for the amount of inconsistency (in a data item) viewed by a query and its e ects on the results of a query. These inconsistencies arise from concurrent updates allowed by ESR. Thirdly, in order to maintain the inconsistencies within bounds associated with each query, the expressions are used to determine the preconditions that operations have to satisfy. The results of a query, and the errors in it, depend on what a query does with the, possibly inconsistent, data viewed by it. One of the important byproducts of this work is the identi cation of di erent types of queries which lend themselves to an analysis of the e ects of data inconsistency on the results of the query. 1 partially supported by the National Science Foundation under grants IRI-9109210 and IRI-9314376. 2 partially supported by NSF, IBM, DEC, AT&T, Oki Electric Ind. and Texas Instruments.