Semistructured data has become prevalent with the growth of the Internet. The data is usually stored in a database system or in a specialized repository. Many information providers have presented their databases on the web as semistructured data, while others are developing repositories for new applications. Designing a “good” semistructured database is important to prevent data redundancy and updating anomalies. In this paper, we propose a conceptual approach to design semistructured databases. A conceptual layer based on the Entity-Relationship model is used to remove redundancies at the semantic level. An algorithm to map an ER diagram involving composite attributes weak entity types, recursive, n-ary and ISA relationship sets, and aggregations to a semistructured schema graph (S3-Graph) is also given.