I was wondering if you could help me with a current issue I am having whilst developing an ER diagram. The problem I am having is with identifying the correct Entities. The scenario I am trying to complete is given below. I have also included a list of entities which I think are needed, however I do not know if these are correct, could you suggest any possible entities and whether the ones I have identified are correct. I have also suggested a few possible relationships please could you assist me in determining whether these are correct.

SCENARIO
A heavy equipment hire company wishes to create a database to monitor the hiring of equipment to clients. The company has two types of equipment: power tools, such as drills and vacuum cleaners, and plants such as excavators and rollers. Power tools are described by their model and the voltage they use, whereas plants are classified by their model and their size in tonnes. The company has various outlets and each outlet has staff including a Manager and several Senior Technicians who are responsible for supervising the work of allocated groups of Technicians. Each outlet has a stock of equipment for hire that may be hired by clients for various periods of time, from a minimum of four hours to a maximum of six months. Each hire agreement between a client and the company is uniquely identified by using a hire number. The company insists that a client must take out an insurance cover for each equipment hire period. Each piece of equipment is checked for faults when it is returned by the client.

The Entities I have identified are as follows:

Equipment
Power Tools
Plants
Company
Outlets
Manager
Senior Technician
Technicians
Client
Hire
Hire agreement
Insurance

Company has * (many) equipment
Equipment has *(many) plants
Equipment has * power tools
Company has 1..* (many) outlets
Outlet has 1..1 manager
Outlet has * (many) senior technicians
Outlet has * (many) technicians
Outlet has for hire * (many) equipment
Outlet has * (many) clients
Client can hire 1..* (one to many) Equipment
Client can have 1..* (one to many) Hire Agreements
Client can have 1..* (one to many) insurance
Hire can have * (many) Hire Agreements
Hire Agreement has * (many) Insurance

As you may have established I am new to the field of ER Diagrams so I apologise for waffling on.

I will be grateful for any help

Regards

The business rules listed are not the structural ones and have to be programmed in by the implementer of the database, you just have to list them.

Business rules:
The company insists that a client must take out an insurance cover for each equipment hire period.
Each piece of equipment is checked for faults when it is returned by the client.
Each outlet has a stock of equipment for hire that may be hired by clients for various periods of time, from a minimum of four hours to a maximum of six months.

Your entities are:

EQUIPMENT
PEOPLE
LOG (which is an intersection entity between EQUIPMENT and CLIENT)
OUTLET
LOCATION
JOB

In EQUIPMENT:
#ID
*Model
SUBTYPES:
POWER_TOOLS
*Voltage
PLANTS
*Size

In PEOPLE:
#ID
*lname
*fname
*DOB
manager_id
job_id (fk References job_id of JOB)
location_id (fk References id of LOCATION)

In LOCATION:
#id
*name

In JOB:
#id
* name

In LOG:
# hire_number
* client_ID
* equipment_ID


If you need help with the relationships, ask, but the one between the subtypes in the EQUIPMENT entity will go to the LOG entity as an arc. It would be easier for me to draw it rather than type it all out.

wow. this gives more info about ER. even im learning about it. thanks a lot