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Chapter 7: Problem 35

Consider requirements for teams, players and games, and develop a suitable ERD. Each team would have a unique name, have a non-player who is the coach, and have several players. Each player has a first and last name and is identified by a number (1, 2, 3, etc.). One player is designated the captain of the team. Assume a game occurs on some date and time, and is played by two teams where one team is called the home team and the other team is called the visiting team. At the end of the game the score must be recorded.

Short Answer

Expert verified
The entities for this exercise are 'Players', 'Teams', 'Games' and 'Coach'. Relationships are 'Players' belong to 'Teams', 'Teams' possess 'Players' and have a 'Coach', and 'Teams' participate in 'Games'. One 'Player' per 'Team' is designated as the Captain. The ERD visually represents these relationships and entities with their attributes and special roles.

Step by step solution

01

Identify Entities

The entities here are 'Players', 'Teams', 'Games' and 'Coach'. Each entity has certain attributes. 'Players' have first name, last name, and number. 'Teams' have a unique name. 'Games' occur on certain date and time. 'Coach' isn't detailed on attributes, but each team has one coach.
02

Identify Relationships

Relationships between these entities can be established. A 'Player' is a part of one 'Team'. A 'Team' can have several 'Players'. Each 'Team' has one 'Coach'. Two 'Teams' participate in a 'Game' - one can be designated as the Home Team and other as Visiting Team. 'Game' holds the Score at the end.
03

Designate Special Roles

It's mentioned that one player is designated the captain of the team. This can be marked as boolean attribute for a 'Player' entity.
04

Create the ERD

Based on the identified entities, attributes, roles, and their relationships, the ERD can be created. It's important to visualize these on a diagram using symbols like circles for entities, lines for relationships and marking attributes next to the entities. Use a different symbol to mark the captain inside the 'Player' entity.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Database Modeling
Database modeling is a pivotal process in creating a structured and organized database system. It involves the representation of complex data structures in a simplified, visual format. In the context of our exercise, database modeling helps us understand how different entities like teams, players, games, and coaches interrelate and how to efficiently store pertinent information.

The core aspects of database modeling include:
  • Understanding Requirements: This means identifying what kind of information we'll be dealing with鈥攕uch as team names, player details, game schedules, and scores.
  • Identifying Entities: Entities are the objects of focus. In our case, teams, players, games, and coaches form the primary entities.
  • Defining Attributes: Each entity has its own unique attributes. For example, a player's attributes are first name, last name, and number.
Through careful database modeling, we ensure that the information is structured logically and efficiently for retrieval and manipulation later in the system.
Relationship Identification
Identifying relationships between entities is essential in representing how entities interact with one another.

In our scenario:
  • Players and Teams: A 'Player' is associated with a single 'Team'. This indicates a many-to-one relationship where many players are part of one team.
  • Teams and Coaches: Each 'Team' has a relationship with one 'Coach', emphasizing a one-to-one pairing.
  • Teams and Games: In 'Games', two 'Teams' are involved, namely the home team and the visiting team. These relationships need careful designation to manage data regarding the game's execution and results.
Understanding and clearly defining these relationships allows us to maintain data integrity and navigate through the data accurately when necessary.
Entity Attributes
Every entity in a database design carries its own specific attributes which describe it in greater detail. Attributes are fundamental in identifying and differentiating one entity from another.

In our example:
  • Players: Include attributes like first name, last name, and a unique number that identifies them.
  • Teams: Have attributes such as a distinct team name, and could include additional details like team formation date or league.
  • Games: Are identified by attributes like date, time, participating teams, and the final score.
Capturing these attributes precisely is crucial for the accuracy of the data. They help provide all the necessary details for each entity, ensuring the system can perform robust queries and reports when needed.
ERD Design Process
The Entity-Relationship Diagram (ERD) design process is an iterative approach that helps in constructing a precise database structure visually. The process involves several key steps:
  • Identify Entities: Begin by determining the main objects or entities, like players, teams, games, and coaches.

  • Define Relationships: Specify how each entity is connected to others, such as player-team, team-coach, and team-game interactions.

  • Determine Attributes: For each entity, list detailed attributes that describe their properties, like player names and game scores.

  • Create the Diagram: Use symbols to visually represent entities as circles or rectangles, with lines to show relationships, and add attributes to these entities. Use symbols to mark special roles like the captain.
The ERD provides a clear, visual map that aids in understanding the schema of a database. It serves as a guide for database developers to implement the necessary structures and relationships effectively. An accurate ERD ensures all data elements are included and correctly linked, assisting further development and database usage.

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Most popular questions from this chapter

Consider an educational institution that has departments and where each department offers courses. Suppose departments are assigned unique identifiers and so deptCode is a key for the department entity type. Courses are identified within a department by a course number; course numbers are unique within a department but not across departments. So, History may have a course numbered 215, and English could have a course numbered 215 too. In order to identify a particular course we need to know the department and we need to know the course number. Illustrate an ERD including department and course entity types. Include attributes for the Department (department code and department name), and for Course (course number, title, and description).

A birthdate attribute would appear for many entity types 鈥� for example students, employees, children. What is a birthdate likely to be: key or non- key?

Suppose a company that sells products has a product entity type with the following attributes: prodNum, prodDesc, prodPrice. Suppose all three attributes are single-valued and that prodNum is a key attribute - each product has a different product number. Illustrate this information in an ERD.

Consider a company that owns and operates parking lots. Draw an ERD to include the following specifications. Each parking lot has a unique address (use the typical fields for addresses) and each parking lot has a certain number, say n, of parking spaces. Each space in a lot has a number between 1 and n. The cost of renting a parking space is the same for all spaces in a lot. The company rents individual spaces out to its customers. Each customer is identified by a driver鈥檚 license id, has a first and last name. Each customer will identify possibly several cars that they will park in the space rented to them. For each car the company needs to know the year, make, model, colour and its license plate number.

Develop an ERD to be used by a company to manage the orders it receives from its customers. Each customer is identified uniquely by a customer id; include the first name, last name, and address for each customer. The company has several products that it stocks and for which customers place orders. Each product has a unique id, unique name, unit price, and a quantity on hand. At any time a customer may place an order which will involve possibly many products. For each product ordered the database must know the quantity ordered and the unit price at that point in time. If the customer does this through a phone call then an employee is involved in the call and will be responsible for the order from the company side. Some orders are placed via the internet. For each order an order number is generated. For each order the database must keep track of the order number, the date the order was placed and the date by which the customer needs to receive the goods.
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