# Rell project structure · Your first Rell app on Chromia · Learn Chromia > Chromia applications are written in Rell, a language built for decentralized applications (dapps). Rell works directly with relational data models, so you… Source: https://chromia.com/learn/book-review/rell-structure/ Your first Rell app on ChromiaLesson 3 of 26 1. [01Your first Rell app on Chromia](https://chromia.com/learn/book-review/introduction/) 2. [02Set up your project](https://chromia.com/learn/book-review/setup/) 3. [03Rell project structure](https://chromia.com/learn/book-review/rell-structure/) Part 1: Define your first entity 1. [04Overview](https://chromia.com/learn/book-review/book-entity/) 2. [05Create your first entity](https://chromia.com/learn/book-review/book-entity/tables/) 3. [06Add your first operation](https://chromia.com/learn/book-review/book-entity/basic-operations/) 4. [07Query every book](https://chromia.com/learn/book-review/book-entity/write-queries/) Part 2: Add a related entity 1. [08Overview](https://chromia.com/learn/book-review/book-review-entity/) 2. [09Define the book review entity](https://chromia.com/learn/book-review/book-review-entity/tables/) 3. [10Add an operation for creating book reviews](https://chromia.com/learn/book-review/book-review-entity/basic-operations/) 4. [11Query all reviews for a book](https://chromia.com/learn/book-review/book-review-entity/write-queries/) Part 3: Checking and validating inputs 1. [12Overview](https://chromia.com/learn/book-review/input-verification/) 2. [13Verify inputs](https://chromia.com/learn/book-review/input-verification/input-verification/) 3. [14Return structured results from queries](https://chromia.com/learn/book-review/input-verification/structure/) Part 4: Signing transactions and filtering queries 1. [15Overview](https://chromia.com/learn/book-review/sign-transaction/) 2. [16Sign a transaction](https://chromia.com/learn/book-review/sign-transaction/sign-transaction/) 3. [17Filter and sort query results](https://chromia.com/learn/book-review/sign-transaction/structure/) Part 5: Blockchain state and transactions explained 1. [18Overview](https://chromia.com/learn/book-review/blockchain-transactions/) 2. [19How blockchain state and transactions work](https://chromia.com/learn/book-review/blockchain-transactions/query-transaction/) 3. [20Walking through an example](https://chromia.com/learn/book-review/blockchain-transactions/example/) Part 6: Create the client 1. [21Overview](https://chromia.com/learn/book-review/build-client/) 2. [22Prerequisites](https://chromia.com/learn/book-review/build-client/prerequisites/) 3. [23Establishing a connection to Chromia](https://chromia.com/learn/book-review/build-client/sign-transaction/) 4. [24Query the blockchain using postchain-client](https://chromia.com/learn/book-review/build-client/query-blockchain/) 5. [25Complete the example](https://chromia.com/learn/book-review/build-client/complete-example/) 1. [26What’s next?](https://chromia.com/learn/book-review/what-next/) [Learn](https://chromia.com/learn/)[Your first Rell app on Chromia](https://chromia.com/learn/book-review/) 03 / 26Beginner # Rell project structure Chromia applications are written in Rell, a language built for decentralized applications (dapps). Rell works directly with relational data models, so you can build reliable blockchain applications in a way that feels familiar and efficient. The [Rell introduction](https://docs.chromia.com/rell/rell-intro) covers the language in more depth. ## Organizing your project You will split the code across dedicated files inside one folder. This keeps the project readable, easy to maintain, and ready to grow. ### Project setup 1. **Add a folder for the main module**: * The project has only one module, so create a folder called `main` under the `src` directory. Every file belonging to the module goes here. 2. **Create the module files**: * Add these files to the `main` folder: + `module.rell` + `entities.rell` + `functions.rell` + `operations.rell` + `queries.rell` You describe your data model in `entities.rell`. Each `entity` in Rell maps to a SQL table, and keywords like `key`, `index`, and `mutable` control how that table is stored and queried. See [Entity](https://docs.chromia.com/rell/language-features/modules/entity) for the full reference. 3. **Declare the module in `module.rell`**: * Put this code in `module.rell`: src/main/module.rell ```nolines module; ``` * The `module;` declaration marks this file as the module's main file. It marks the folder as a module, so Rell treats all files in it as one unit, which keeps your code organized and easier to manage. 4. **Remove the old `main.rell` file**: * The `src` folder already contains `main.rell`. You could keep all your code in that single file, but separate files make the structure easier to follow. Delete `main.rell` to complete the reorganization. The project should now have this layout: text ``` book-review/ ├── src/ │ ├── main/ │ │ ├── entities.rell │ │ ├── functions.rell │ │ ├── module.rell │ │ ├── operations.rell │ │ └── queries.rell │ └── test/ │ └── book_review_test.rell ├── .gitignore └── chromia.yml ``` Each file has a single responsibility, which keeps the codebase manageable as the application grows. The next sections go through these files one at a time, beginning with entity definitions and building up to a complete decentralized application. Written for this site from Chromia’s public course. Code samples are the course’s own. [← Previous**Set up your project**](https://chromia.com/learn/book-review/setup/)[Next →**Part 1: Define your first entity**](https://chromia.com/learn/book-review/book-entity/) On this page * [Organizing your project](#organizing-your-project)