### Instruction:
Build a BlueBream-based web application that manages a simple inventory system. The application should support adding, updating, and deleting items with fields such as item name, description, quantity, and price. Use PostgreSQL as the database backend.

### Response:

To build a BlueBream-based web application that manages a simple inventory system, follow these steps:

1. Install the required packages and set up the environment.

First, you need to install Python 3.x, PostgreSQL, and virtualenv on your machine if they are not already installed.

Next, create a new directory for your project and navigate into it:

```
$ mkdir bluebream_inventory
$ cd bluebream_inventory
```

Create a virtual environment and activate it:

```
$ python3 -m venv env
$ source env/bin/activate
```

Install BlueBream and psycopg2 (PostgreSQL adapter for Python) in the virtual environment:

```
(env) $ pip install bluebream psycopg2
```

2. Create a new BlueBream project.

Use the `paster` command to create a new BlueBream project called "inventory":

```
(env) $ paster create -t bluebream inventory
```

Navigate into the newly created project directory:

```
(env) $ cd inventory
```

3. Configure the database connection.

Edit the `configure.zcml` file located at `src/inventory/configure.zcml`. Add the following lines inside the `<configure>` tag:

```xml
<include package="zope.sqlalchemy" />
<include package="psycopg2" />

<utility
    name="inventory_db"
    provides="zope.sqlalchemy.interfaces.IDataManager"
    component=".db.InventoryDataManager"
/>
```

4. Set up the SQLAlchemy models and data manager.

Create a new file named `db.py` inside the `src/inventory` folder with the following content:

```python
from sqlalchemy import create_engine, Column, Integer, String, Float
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import scoped_session, sessionmaker
from zope.sqlalchemy import ZopeTransactionExtension
from zope.sqlalchemy.interfaces import IDataManager

DBSession = scoped_session(sessionmaker(extension=ZopeTransactionExtension()))
Base = declarative_base()

class InventoryItem(Base):
    __tablename__ = 'inventory'
    id = Column(Integer, primary_key=True)
    name = Column(String(100), nullable=False)
    description = Column(String(255))
    quantity = Column(Integer, default=0)
    price = Column(Float, default=0.0)

class InventoryDataManager:
    implements(IDataManager)

    def __init__(self):
        self.engine = create_engine('postgresql://username:password@localhost/dbname')
        DBSession.configure(bind=self.engine)

    def getSession(self):
        return DBSession
```

Replace `username`, `password`, and `dbname` with your PostgreSQL credentials.

5. Create the database tables.

Run the following command to create the necessary tables in your PostgreSQL database:

```python
(env) $ python -c "from inventory.db import Base, InventoryDataManager; \
                  manager = InventoryDataManager(); \
                  Base.metadata.create_all(manager.engine)"
```

6. Implement views for adding, updating, and deleting items.

Create a new file named `views.py` inside the `src/inventory` folder with the following content:

```python
from pyramid.view import view_config
from .db import InventoryItem, InventoryDataManager

manager = InventoryDataManager()
session = manager.getSession()

@view_config(route_name='add_item', renderer='json', request_method='POST')
def add_item(request):
    item = InventoryItem(**request.json_body)
    session.add(item)
    session.flush()
    return {'id': item.id}

@view_config(route_name='update_item', renderer='json', request_method='PUT')
def update_item(request):
    item_id = int(request.matchdict['id'])
    item = session.query(InventoryItem).get(item_id)
    if item:
        for key, value in request.json_body.items():
            setattr(item, key, value)
        session.flush()
        return {'status': 'success'}
    else:
        return {'status': 'error', 'message': 'Item not found'}

@view_config(route_name='delete_item', renderer='json', request_method='DELETE')
def delete_item(request):
    item_id = int(request.matchdict['id'])
    item = session.query(InventoryItem).get(item_id)
    if item:
        session.delete(item)
        session.flush()
        return {'status': 'success'}
    else:
        return {'status': 'error', 'message': 'Item not found'}
```

7. Configure the routes.

Edit the `configure.zcml` file located at `src/inventory/configure.zcml`. Add the following lines inside the `<configure>` tag:

```xml
<route
    name="add_item"
    path="/items/add"
/>

<route
    name="update_item"
    path="/items/update/{id}"
/>

<route
    name="delete_item"
    path="/items/delete/{id}"
/>
```

8. Run the application.

Start the BlueBream server with the following command:

```
(env) $ paster serve src/inventory/development.ini --reload
```

Now you can use your favorite HTTP client or web browser to interact with the inventory system by sending requests to the `/items/add`, `/items/update/{id}`, and `/items/delete/{id}` endpoints.