If you begin the data model using a use case look at

Info icon This preview shows pages 50–61. Sign up to view the full content.

View Full Document Right Arrow Icon
If you begin the data model using a use case , look at the major inputs and outputs of the use case. If the process models are available, look at the data stores, external entities, and data flows.
Image of page 50

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Attributes & Identifiers Information that describes each entity becomes its attributes . Check in the CASE repository of the process model for details on data flows and data stores. Check the data requirements of the requirements definition. Use requirements elicitation techniques (e.g., interview and document analysis). One or more of the attributes will become the entity’s identifier .
Image of page 51
Identify Relationships The last step in creating ERDs is to determine how the entities are related to each other. Lines are drawn between the entities that have relationships . Each relationship is labeled, and cardinality and modality are assigned.
Image of page 52

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Independent vs. Dependent Independent Entity Can exist without the help of another entity Identifiers are created from the its own attributes Dependent Entity Child entity does require attributes from the parent entity to uniquely identify an instance. Its identifier consists of at least one attributes from the parent entity.
Image of page 53
Intersection Entity Represents information about the relationship between two other entities. Typically to explain two entities sharing an M:N relationship. 1. Remove the M:N relationship line and insert a new intersection entity between the two existing 2. Add two 1:N relationships to the model. 3. Name the intersection entity.
Image of page 54

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
55
Image of page 55
DFD vs. ERD Data flows and data stores are comprised of data elements Data elements of a data flow moving in or out of a data store must be a subset of the data elements in that data store. Transformations occur only in processes.
Image of page 56

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
DFD vs. ERD Entities on an ERD often (but not always) correspond to data stores on a DFD Attributes on an ERD usually correspond to data elements (listed in the data dictionary) that make up the data store and data flows on a DFD Relationships on an ERD do not correspond to processes on a DFD Sources and sinks on a DFD usually do not show up as entities on an ERD
Image of page 57
58 DFD Incorrect ERD Menu Selection NOTE: Known flow control problem Cook Customer Inventory Places Order Name Hours Name Address Item Quantity Customer Cook Inventory Processing 1.0 Take Order 2.0 Convert Order to Cooking Instructions 3.0 Convert Order to Ingredient List Processed Order D1 Order Log Cooking Instructions Ingredients
Image of page 58

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
59 Correct ERD DFD Menu Selection NOTE: Known flow control problem Customer Cook Inventory Processing 1.0 Take Order 2.0 Convert Order to Cooking Instructions 3.0 Convert Order to Ingredient List Processed Order D1 Order Log Cooking Instructions Ingredients Order Item Ingredient Cooking Instructions Contains Includes Requires OrderId Date Time ItemId ItemName StepId Description Description ItemQuantity Ingredient Quantity Index
Image of page 59
Balance with DFDs The process models and data models are interrelated.
Image of page 60

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 61
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern