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Say there are two modules users and status. I split these modules in following 2 cases
Here is case-1
Here is case-2
I am trying to understand which database design lowly coupled and should be adopted according to the Software Engineering Design principals? Particularly interested to have comments that which approach is better by considering re-usability. I mean in future which approach can be re-used easily & effectly to any other software design
Both your cases have consistency issues rather than coupling/cohesion issues.
First, both your cases allow for a department to have a limitless amount of statuses. This might not make sense if, for instance, the status represents whether the department is open or closed. If departments may only have 1 status at any given time, your primary key for an status must be dept_id (in which case it should be within the departments table as a foreign key to the table with the available statuses instead), this may be incorrect depending on what you are modelling. The second case, however, is worse for consistency because it allows you to have an unlimited amount of values for the variable status (There is no table to define the valid values for status, so this case allows you to have typos even, for instance a department with status "opne" instead of "open")
Secondly, the users table has no relationship with the rest of the data, which may not make sense again (users can't be members of any department, etc). In the first case, users have no status and in the second case it is related to an status table... Neither case (for the users table) has more or less coupling than the other (because it has no relationship with anything else in your model), but you need to check whether you want users to have an status (and what is that status, whether it should be selected from a fixed list of values or not).
We don't have much to go on about analyzing coupling/cohesion in both of your cases. You must better understand what you are trying to model and should first worry about ensuring consistency.
Here's an short but interesting blog post about coupling/cohesion if you want to read some: https://thebojan.ninja/2015/04/08/high-cohesion-loose-coupling/
Hope it helps!
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I'm redesigning our service app, and getting rid of some really awful schema problems while I'm at it. Trying to build the replacement with best practices as much as possible.
I'm having a company table rather than just customer, as it's often useful to identify companies that are not customers (suppliers, contractors, etc etc). I'm trying to decide whether it's better to simply include a boolean field represented in the relevant part of the app by a checkbox that identifies relevant companies as customers (which would become uneditable once the customer has services attached to them), or if I should, instead, have a separate table that's basically just a single field referencing the Company ID that is in turn referenced by any child records.
This similar question asks about records that can be one of several subtypes. While the question is materially different (every policy seems to be only one of the potential subtypes, whereas Companies can be any or all of Customer/Supplier/Contractor etc) its similarity combined with the fact that it has multiple conflicting answers raises the possibility that there is no industry-wide consensus, so:
Is there an established best practice here? I'm not immediately seeing any reasons that other fields should be included in the prospective Customer table, but I'm open to the idea that there might... is that a good enough reason to go with B? Or is this a clear YMMV situation, where both options have benefits, either being equally valid?
I should, instead, have a separate table that's basically just a single field referencing the Company ID that is in turn referenced by any child records.
There are probably several attributes that apply to a customer that don't apply to a non-customer Company, so CompanyID probably won't end up being the only attribute of Customer.
So if that's the case, the clear choice is to have a separate Customer table.
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For background, my situation is I have a database that is missing a lot of foreign key relationships. One in particular, let's call it Orders, which represents orders with a composite primary key of OrderID and LocationID. The other table we'll call OrderDetails which has an OrderID but no LocationID. In reality, it is impossible to have an order in two locations at once, so it was assumed that there was no need to have LocationID in the details table. I didn't design it, and I can't change that.
We also have to work under the assumption there will be no support to add location id to the details table for various reasons. We are also working with Oracle and a high volume database with many concurrent users in many locations. Finally, there will be minimal time to change any applications that use this table.
So my question is: is this solution is feasible, or is there anything else I should try?
Say I create an intersection table, for lack of a better name AllOrders or whatever with primary key OrderID. Now we link Order.OrderID to AllOrders.OrderID and link OrderDetails.OrderID to AllOrders.OrderID. Would it be reasonable then to fill in AllOrders via a trigger on each insert to Orders to enforce the integrity? I am assuming all applications are inserting details after orders or the changes to enforce would be minimal and allowed.
Are there any better solutions? I understand we would do this differently if in charge of designing or given more leeway for fixing, but I'm trying to make the most given the constraints.
Edit --
To clarify what I am looking to accomplish, I want to treat all orders with the same ID as an equivalence class modulo location and ensure that if any order is deleted it requires all orders with the same id deleted and all child order details to be deleted. With primary importance of no orphan details. This has to be done with minimal application changes if possible and no redesign of existing tables if possible.
Create a new table to handle the mapping going forward.
Table: Tb_order_orderdetails
Columns: OrderID, LocationID, OrderDetailsID
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I'm learning how to design databases, and i've been ask to create the table that will hold this form: Medical History I'm learning to use Django/Python i've already made the markup in HTML and CSS, but I don't think that making each question on the form an column would be the best approach. For example in the family history i've thought of making it a separate table, while in the review of systems i want to make each to be a set.
A pragmatic approach is to define tables based on the following criteria:
1) easy to select data from them (not to obtain many JOINs or convoluted queries that require ORs or strings splitting)
2) easy to understand (each concept maps to one table)
=> usually, normalized structures do the trick here
Of course, above are challenged in high transactional environments (INSERTs, UPDATEs, DELETEs).
I would assume then your case has moderate INSERTs, but more SELECTs (reports).
For Family history section I would normalize everything:
DiseaseType
DiseaseTypeId
Code -- use to separate from a name that can change in time
Name -- breast cancer, colon cancer etc.
CollateralOption
CollateralOptionId
Code -- I would put UNIQUE constraints on Codes and Names
Name -- no, yes, father
FamilyHistory
FamilyHistoryId INT PK IDENTITY -- this may be missing, but I prefer if I use an ORM
PatientId -> FK -> Patient
DiseaseTypeId -> FK -> DiseaseType
CollateralOptionId FK -> CollateralOption
Checked BIT -- you may not define this and have records for Checked ones.
-- having this may put some storage pressure
-- but prevent some "stuffing" in the queries
These structures allow to easily COUNT number of patients with colon cancer cases in their family, for example.
Shortly put: if there is not serious reason against it, go for normalized structures.
I don't see any advantage to perform any design tricks on this data structure. Yes, making a boolean attribute of each of your checkboxes, and a string attribute of each of your free texts, will lead to a high number of attributes in one table. But this is just the logical structure of your data. All these attributes are dependent on the key, some person id, (or at least that's what I assume, as a medical layman). Also, I assume that they are independent of each other, i.e. not determined by some other combination of attributes. So they go to the same table. Putting them on several tables won't gain anything, but will force you to do lots of joins if you query on different types of attributes (like all patients whose mother had breast cancer and who now have breast lumps).
I don't know exactly what you mean by making sets of some attributes. Do you mean to have just one attribute, and encode the sequence of boolean values e.g. in one integer, like 5 for yes-no-yes? Again that's not worth the trouble, as it won't save any space or whatever, but will make queries more complicated.
If you are still in doubt, try to formulate the most frequent use cases for those data, which will probably be typical queries on combinations of these attributes. Then we might see whether a different structure would make your life easier.
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I have a database design issue, one that has rattled my brain.
What is the project?
I am designing a platform where different people register a group, each group is allowed to register their own members, it is important to keep these groups away from each other, as each are to their own, each group would have access to 65 or more tables with possibilities of 1000 of rows of data in each table, in their own database, each database is a copy of an empty master database.
Where i am stuck.
I do not know if this is wise cause i could end up with a 1,000 - 30,000 databases. I need to either create a database with a unique name (scenario above) or create a database with a unique environment variable, where each group has it's own environment variable.
Where things get messy.
Assigning each group to a unique database allows me to keep things simple, allows me to access all the data within the group relatively easy (vs searching through 1000 of groups data in one database). a simple but not too important, but still relevant eg. Each group can create things like their own invoices, so if all groups have unique databases then the invoice numbers would follow logically (users perspective), but if all groups are within the same database invoice numbers would not follow logically (users perspective).
The Question Then
Should I, or would it be wise, to create multiple database to keep my system efficient, bear in mind that there is no need to cross over from one group to another.
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I'm working with Ruby on Rails, but this question I think is broader than that and applies to database design generally.
When is it a good idea to split a single model up into multiple tables? For example, assume I have a User model, and the number of fields in the model is really starting to add up. For example, the User can enter his website, his birthday, his time zone, his etc etc.
Is there any advantage or disadvantage to splitting up the model, such that maybe the User table only has basic info like login and email, and then there is another table that every User has that is something like UserInfo, and another that is UserPermissions, and another that is UserPrivacySettings or something like that?
Edit: To add additional gloss on this, most of the fields are rarely accessed, except on pages specific to them. For example, things like birthday are only ever accessed if someone clicks through to a User's profile. Furthermore, some of the fields (which are rarely accessed) have the potential to be extremely large. Most of the fields have the potential to be either set to blank or nil.
Generally it is a good idea to put things which have a one-to-one relationship in the same table. Unless your userbase includes the Queen or Paddington Bear, a user has just one birthday, so that should be an attribute of the USERS table. Things which have a one-to-many relationship should be in separate tables. So, if a user can have multiple privacy settings by all means split them out.
Splitting one table into several tables can make queries more complicated or slower, if we want to retrieve all the user's information at once. On the other hand if we have a set of attributes which is only ever queried or updated in a discrete fashion then having a separate table to hold that data is a sound idea.
This would be a situation for analysis.
When you find that a lot of the fields in such a table are NULLs, and can be grouped together (eg. UserContactInfo), it is time to look at extracting the information to its own table.
You want to avoid having a table with tens/hundreds of fields with only sparsely entered data.
Rather try to group the data logically, and crete the main table containging the fields that are mostly all populated. Then you can create subsets of data, almost as you would represent them on the UI, (Contact Info, Personal Interest, Work Related Info, etc) into seperate tables.
Retrieving a row is more expensive if it has many columns, especially if you usually need just some of the fields. Also, hosting stuff such as the components of an address in a separate class is a case of DRY. On the other hand, if you do need all fields of an object, it takes longer to execute a compound query.
I would normally not bother to distribute classes over several tables just to make the code more readable (i.e. without actually reusable parts like addresses).