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ERD Diagram for Property Management

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  • ERD Diagram for Property Management

    Please help me verify my attached ER diagram.

    I am building a Work Order module and so far have defined the following entities:

    1) USERS Each USER can access one or more COMPANIES
    2) COMPANY - Each COMPANY can have one or more PROPERTIES
    3) PROPERTY Each PROPERTY has multiple apartment UNITS
    4) UNIT Each apartment UNIT can have multiple rental APPLICATIONS
    5) APPLICATION - Each rental APPLICATION can results in 1 LEASE
    6) LEASE Each LEASE have 1 TENANT (occupants listed separately)
    7) TENANT Each TENANT can have multiple TICKETS to report problems
    8) TICKET Each problem TICKET can have multiple WORKORDER
    9) WORKORDER Signed off upon repair job completion

    I have defined a 1:n Identifying Relationship for all entities except LEASE and TENANT (1:1 Identifying Relationship), this resulted in a 7 levels deep cascading reference for the last entity WORKORDER. So by the time I got to the last table WORKORDER, it wound up with the following PKs & FK. With the exception of the very 1st key, everything else is generated by MySQL Workbench:

    Primary Keys Fields (all are INT, Auto increment)
    -------------------------------------------------

    ID (WORKORDER_ID) - The only column I specified
    TICKET_ID
    TICKET_TENANT_ID
    TICKET_TENANT_LEASE_ID
    TICKET_TENANT_LEASE_APPLICATION_ID
    TICKET_TENANT_LEASE_APPLICATION_UNIT_ID
    TICKET_TENANT_LEASE_APPLICATION_UNIT_PROPERTY_ID
    TICKET_TENANT_LEASE_APPLICATION_UNIT_PROPERY_COMPANY_ID

    Foreign Key
    -----------

    WORKORDER_TICKET

    This seems normalized to me but since I am no expert in normalization it worries me a lot because it looks a bid crazy. I'd greatly appreciated if some experts here can comment on the correctness of my ERD design and also comment on performance and other future implications as it pertains to MySQL and Alpha Five.
    Attached Files
    Last edited by rchen2001@hotmail.com; 08-14-2011, 06:27 PM.

  • #2
    Re: ERD Diagram for Property Management

    I wouldn't worry too much about Normalisation.
    Once Normalised, it might be as well to Rationalise - i.e. make the application easier to maintain in the future.
    It's an easy biuld in Alpha so why not give it a go and prove the design concept?
    Ted Giles
    Example Consulting - UK
    .

    sigpichttp://ec12.example-software.com//
    See our site for Alpha Support, Conversion and Upgrade.

    Comment


    • #3
      Re: ERD Diagram for Property Management

      While normalization makes databases more efficient to maintain, they can also make them more complex because data is separated into so many different tables.
      and
      Third Normal Form (3NF): No duplicate information is permitted.
      As Ted said - rather design for easier application maintenance.
      Honestly, I would suggest you first define your Entity Tables, use the ERD only to establish the linking fields .
      Normalization doesn't apply to ERDs but to database design. Use your knowledge of the flow of data (practical workflow) to create logical forms and let sets do the ER for you. Then focus on tables to handle billing and other event records.

      Comment


      • #4
        Re: ERD Diagram for Property Management

        Thanks for the reply. Perhaps I should have mention this is only one of the many modules for this project, the entire system will have about 50-80 tables. You are right I might as well just build it base on my ERD and see what happens. But it will be hard to gauge future performance and other implications if ERD is flawed, this is why I wanted to be sure of the schema. Any thoughts on the ERD?

        Comment


        • #5
          Re: ERD Diagram for Property Management

          Originally posted by rchen2001@hotmail.com View Post
          ... this is only one of the many modules for this project, the entire system will have about 50-80 tables.... Any thoughts on the ERD?
          In which case you have a partial ERD. Forget terminology, you seem to know what you want. An ERD is mostly fact - what relates to what, you have limited flexibility there. Performance is based on the database design, which you are not as strictly committed to - whatever you do that is inefficient can (usually) be redesigned.

          Comment


          • #6
            Re: ERD Diagram for Property Management

            One of the systems I work with has 2700 tables, of which 47 are used regularly. It's a pig - but not my pig thankfully.
            I created an Alpha app to construct Questions and Answer options to load into a highly normalized Oracle dataset. Doing it using Toad took far too long as so many tables needed to be addressed in a complex sequence. BT wanted it in ASP and C#. Took me a week and their developer 4
            Months.
            If this is an ongoing dev. build yourself a DD to handle things.
            Ted Giles
            Example Consulting - UK
            .

            sigpichttp://ec12.example-software.com//
            See our site for Alpha Support, Conversion and Upgrade.

            Comment


            • #7
              Re: ERD Diagram for Property Management

              Originally posted by Ray in Capetown View Post
              In which case you have a partial ERD. Forget terminology, you seem to know what you want. An ERD is mostly fact - what relates to what, you have limited flexibility there. Performance is based on the database design, which you are not as strictly committed to - whatever you do that is inefficient can (usually) be redesigned.
              I think redesigning is my biggest concern. I am not very fond of redesigning after years of redesigning poorly conceived projects (not entirely my fault, clients are often partially to blame)
              But I suppose with Alpha it's much quicker and easier.

              So what would you suggest Ray? Just define and create the tables according to my knowledge of business logic, then using sets or linked content to create the links as needed?

              Comment


              • #8
                Re: ERD Diagram for Property Management

                Originally posted by Ted Giles View Post
                One of the systems I work with has 2700 tables, of which 47 are used regularly. It's a pig - but not my pig thankfully.
                ..
                If this is an ongoing dev. build yourself a DD to handle things.
                That is a fat pig! In comparison my 150 tables PowerBuilder app is just a hamster. No I don't intend on working on this forever, like 5 months and move on. What's a DD Ted?

                Comment


                • #9
                  Re: ERD Diagram for Property Management

                  I would say yes to that exactly - get it going without all the frills and cosmetics to prototype this segment. See that things will connect on forms and appear logical. Make copy forms to play around with concepts, and number them.. stuff like that. And then when you hit blocks ask relevant questions. IMO you passed the point of asking the board to comment on design, I don't know exactly what you want to achieve.

                  Comment


                  • #10
                    Re: ERD Diagram for Property Management

                    The client already seen and approved the prototype demo. It's the real deal now so hopefully not too much looking back. You are right, with Alpha it's really not that big a deal to go back and modify as long as the DB is fundamentally sound. I feel so much more confident to proceed now. Thanks again for your help!

                    Comment


                    • #11
                      Re: ERD Diagram for Property Management

                      A DD is a Data Dictionery. You can use it to get your thoughts together and agree the connections/keys/etc.
                      I'm going to build a basic one and post it on the Forum. I'll put it here first, and I'll be starting in a few minutes so it's likey to be available tomorrow.
                      What it does is help to get the ducks in a row.
                      To do this it helps create Tables as you can add the Fields and the Field Rule comments - it doesn't build actual Rules.
                      Once you have the design for each Table, you can create it using the Text version for Table creation.

                      Glad you got the job from a Prototype - always the best way. When I got my first "biggie" I thought "Whoopie - Oh Bu66er - now I've got to do it!"
                      Ted Giles
                      Example Consulting - UK
                      .

                      sigpichttp://ec12.example-software.com//
                      See our site for Alpha Support, Conversion and Upgrade.

                      Comment


                      • #12
                        Re: ERD Diagram for Property Management

                        Thanks Ted for all your help. My thoughts were pretty clear before I got involved with that ERD, then I got all concerned with too many theoretical and practical implications of 3NF. The more I research the more issues comes up lol. You guys really helped me clear my head. Much obliged.

                        Comment


                        • #13
                          Re: ERD Diagram for Property Management

                          Is this a desktop app or a web app?

                          I'm curious how Ted's DD applies to MySQL?

                          FYI: I've had difficulties using a db schema created in WorkBench and using it with linked grids. Somehow the MySQL linkage and the grid linkage conflicts - at least in my experience.
                          Peter
                          AlphaBase Solutions, LLC

                          Peter@AlphaBaseSolutions.com
                          https://www.alphabasesolutions.com


                          Comment


                          • #14
                            Re: ERD Diagram for Property Management

                            This is a web app. I'll take that WorkBench / Grid linkage conflict into consideration. Thanks Peter.

                            Comment


                            • #15
                              Re: ERD Diagram for Property Management

                              Well this might scupper the plan.
                              The Tables can be uploaded into SQL I believe, but the attached DD is really a Desktop design aid item.
                              It's an ongoing free development with a Bug button to mail me.
                              Login is AUser
                              Password is Guest.

                              If you are watching Stan, I'd appreciate a bit of help with the table_create feature code.
                              Attached Files
                              Ted Giles
                              Example Consulting - UK
                              .

                              sigpichttp://ec12.example-software.com//
                              See our site for Alpha Support, Conversion and Upgrade.

                              Comment

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