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TerraER - Entity-Relationship Modeling Tool

Henrique Rocha, Ricardo Terra

TerraER is a free open-source learning tool designed to aid students in the creation of entity-relationship models. Our main goal is to provide students with a tool that reflects exactly the data modeling concepts learned in the classroom.

Web Site:
Version tested: TerraER 2.02
System requirements: Java 1.5 or higher
License & Pricing: Open Source GNU Public License, Freeware.
Support: Documentation available at our website and issue tracker system at


Data modeling is one part of the database conceptual design process. The entity-relationship model (ER model) is a largely used conceptual model proposed by Chen [1]. It defines the entities and the relationships between these entities. The ER model is simple and easy to understand, making it intelligible to both database designers and end users [2, 3, 4].

Academic database courses still adopt ER models to teach conceptual design. Nevertheless, we noticed a lack of modeling tools for this purpose. In practice, most modeling tools support logical design, which is a detailed model the designer proceeds after the conceptual model is complete. In view of such circumstances, academics (students and professors) are forced to use logical design tools instead, such as DBDesigner, ERWin, etc.

The use of existing logical design tools - rather than conceptual design ones - has two major issues: (i) they may confuse students who are learning about conceptual modeling; and (ii) they were not developed for academic purposes. To address these shortcomings, we designed TerraER, a free open-source learning tool designed to aid students in the creation of ER models. Our main goal is to provide students with a tool that reflects exactly the data modeling concepts learned in the classroom.


TerraER is distributed in a single JAR file publicly available for download at our web site The JAR file is auto-contained, i.e., it can be placed in any folder, does not require the installation of additional libraries, and does not change operating system files (e.g., windows registry). In a nutshell, TerraER requires only a Java Runtime Environment (JRE) previously installed on the target computer (

Main Features

TerraER 2.02 has the following relevant features:

  • Free and open-source (GPL);
  • Simple and small but complete application (around 5 MB);
  • Cross-platform (only needs a JRE);
  • Internationalization (English and Portuguese);
  • Persist models to XML files (a cross-platform format);
  • Clipboard transfer;
  • Model printing; and
  • Easy to learn and intuitive interface.

User Interface & Feature description

TerraER was initially designed for academic purposes, i.e., to help students and professors in the task of creating ER models. Therefore, we developed the graphical user interface to be practical, intelligible, and intuitive (i.e., easy to learn and use).

The tool is a free, open-source application under the GNU Public License. Thereupon, we encourage users to directly contribute to the TerraER project ( As an example, a B.Sc. student has contributed to the project by developing the internationalization for the English language.

Entity-Relationship Modeling Tool

Figure 1 - Screenshot of TerraER 2.02 modeling a hypothetical Banking ER

The tool is developed in Java language, which makes TerraER a cross-platform application. In addition, new releases are always verified on Windows, Linux, and Mac OS.

Figure 1 illustrates the TerraER interface, which is organized into five main parts:

  1. Menu bar: It provides the users with basic functionalities, such as saving, loading, and printing the models. More important, the models are saved in an XML-based format, which directly contributes to the cross-platform feature. In practice, models saved using an operating system can be loaded on a different one without any issue;
  2. Objects toolbar: It provides commands to create ER model elements - such as entities, relationships, attributes, etc. - on Chen's notation, as adopted by Elmasri and Navathe [3];
  3. Position toolbar: It provides users with means to manipulate elements' position - such as alignment, overlapping, etc. - in order to support an elegant model design;
  4. Object inspector: It lists the elements of the current ER model and allows user to select, remove, or edit them. In practice, this feature provides a quick and precise way to handle model's elements;
  5. Drawing area: It shows the graphical view of the ER model under creation. The user may add and remove elements to the model. There is a zoom feature, which can be very useful when dealing with large models. Also, there is a grid feature that displays a grid to help users to position elements.

Evaluation Experiment

TerraER was initially designed as a teaching aid tool for academic database courses. In order to evaluate the applicability of our tool, we conducted a study in a Brazilian university to obtain the feedback from undergraduate students, which represent our target public.

In the study, we defined three assignments and divided the database course class in 10 groups. In the first assignment, five groups were required to use DBDesigner (a popular database design system) and the other five groups to use TerraER. In the second assignment, we swapped the groups. In the third and last assignment, each group could opt for which tool they prefer. In the last day of the class, the students filled an evaluation form.

The results clearly indicate a preference for TerraER as the model design tool. In fact, nine out of ten groups preferred TerraER to DBDesigner. According to the answers of the evaluation forms, the students argue that TerraER is easier to use and understand because it reflects the conceptual design learned inside the classroom.

Supporting TerraER

We welcome any help from the open-source community to support TerraER. For those not comfortable with their programming skills, it is possible to contribute with suggestions, donations, and even helping in the creation of a better documentation. TerraER source-code is available at <>, for those willing to play a more active roll.


Academic courses still adopt ER model for database modeling. However, there is a severe lack of tools designed for this particularly purpose. In view of such circumstances, academics (professors and students) do not have other option than to rely on tools that do not follow the concepts learned inside the class. Even though these are usually popular tools, they do not draw conceptual models but logical models instead. In practice, it may negatively impact the learning curve of the students.

To address this shortcoming, we developed TerraER with the specific purpose to be adopted in academic courses. Thereupon, we made the tool simple, easy to use, and complete w.r.t. ER modeling using Chen's notation. More important, the study we conducted has shown students' preference for TerraER because it reflects the concepts learned in the classroom.

Last but not least, TerraER is a small, multi-platform, free, and open-source software system, which make the tool the proper choice for conceptual data modeling. As far as we can guarantee, TerraER is currently (2013-year) employed in databases courses in ten Brazilian universities.


[1] P. P. Chen. The entity-relationship model - towards a unified view of data. ACM Transactions on Database System, pages 9-36, 1976.

[2] S. Bagui and R. Earp. Database Design Using Entity-Relationship Diagrams. CRC Press LLC, 1964.

[3] R. Elmasri and S. B. Navathe. Fundamentals of Database Systems. Addison-Wesley, 6th edition, 2010.

[4] A. Silberschatz, H. F. Korth, and S. Sudarshan. Database System Concepts. McGraw-Hill, 6th edition, 2010.

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This article was originally published in the Fall 2013 issue of Methods & Tools

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