and presented his ER model in the First Very Large Database Conference in September 1975, the same year of a paper with similar concepts written by A. P. G. Brown. Chen's main contributions are formalizing the concepts, developing a theory with a set of data definition and manipulation operations, and specifying the translation rules from the ER model to several major types of databases (including the Relational Database). He also popularized the model and introduced it to the academic literature. The ER model was adopted as the meta-model ANSI Standard in Information Resource Directory System (IRDS), and the ER approach has been ranked at the top methodology for database design and one of the top methodologies in systems development by several surveys of Fortune 500 companies. Computer-aided software engineering Chen's work is a cornerstone of software engineering, in particular computer-aided software engineering (CASE). In the late 1980s and early 1990s, IBM's Application Development Cycle (AD/Cycle) framework and DB2 repository (RM/MVS) were based on the ER model. Other vendors’ repository systems such as Digital's CDD+ were also based on the ER model. Chen has had a significant impact on the CASE industry through his research and his lecturing around the world on structured system development methodologies. The ER model has influenced most of the major CASE tools, including Computer Associates’ ERWIN, Oracle Corporation’s Designer/2000, and Sybase’s PowerDesigner (and even a general drawing tool like Microsoft Visio), as well as the IDEF1X standard. The ER model is also the basis for Microsoft's ADO.NET Entity Framework. The hypertext concept, which makes the World Wide Web extremely popular, is very similar to the main concept in the ER model. Chen investigated this linkage as an invited expert of several XML working groups of the World Wide Web Consortium (W3C). The ER model also serves as the foundation of some of the recent work on Object-oriented analysis and design methodologies and Semantic Web. The UML modeling language has its roots in the ER model. Computer performance modeling In his early career, he was active in R&D activities in computer system performance. He was the program chair of an ACM SIGMETRICS conference. He developed a computer performance model for a major computer vendor. His innovative research results were adopted in commercial computer performance tuning and capacity Memory and storage hierarchy, storage technology, CD-ROM, firmware, and micro-programming His Ph.D. thesis at Harvard was one of the first