The availability of data in different datasources increases highly the demand on accessing this data in a uniform and generalised way, especially in decision making applications which require an exhaustive investigation and examination of the data. The data quality represents an essential characteristic requested by the users, particularity with the arrival of the data integration systems (DIS) which integrate data from multiple datasources and present them to the users as single database. This paper discusses the data quality evaluation in DIS systems. Precisely, it addresses the issues of the quality evaluation of the data delivered to the end users as results to their queries and the verification of the achievement of users' quality expectations. Besides, it analyses how to improve the DIS systems by using quality scales and to enforce data quality. We propose to study one quality attribute, to analyse its effect in a DIS system, and to suggest methods for its assessment. Between the quality attributes that have been defined, this paper investigates the more significant one which is data freshness.