I have no problem with converting ER to SQL tables, but I don't know how can I convert EER to SQL tables?
as you Know that EER has "is a" specification and inheritance, but I don't know how relational databases can connect with inheritance specification
I'm not sure how to convert all the EER to SQL table in one user action, but this should work:
Right click on a table,
Copy the table creation script to clipboard,
Paste this script in the shell command.
This will create the table.
Hope this helps.
I'd say look into the Hibernate storage strategies.
Hibernate is an ORM system that persists objects in an SQL database. In the link that I sent you it gives you a table schema for how the storage strategy is persisted in the SQL database.
If you use Appfuse or Groovy it can generate these relationships for you.
Then you might want to map the schema into a CASE tool of some sort to turn it into an Entity Relationship Diagram.
Simplest answer is:
The subtype table will use id of supertype as their id. This will guarantee subtype 'is a' supertype, instead of subtype 'is associated with' super type.
There are other rules for you to convert EERD generalization/specialization hierarchies (if you are interested, reply and I will send you a link to learn about all rules). However, most of the cases, following two rules are going to work
Create a relation for a supertype, create each relation for each subtype, id of the subtype relation is the id of the supertype relation (this option generally work for all cases). Store all common attributes in the super relation, store only special attributes in the subtypes.
For "Disjoint Mandatory Specialization/Generalization Hierarchy", you could have the option to create a table for each subtype (without having to create a relation for the supertype).
Hope this helps.
Related
Say I have two query types, they both have a key column (as it happens, I'm querying an SCCM database by its views) called ResourceID.
The way I read the documentation this may not be possible since a Query Type cannot be the principal end of a relationship.
Can anyone confirm/deny this?
I don't think specifics are required for this question, but if you feel they are I can add some.
Yes! You cannot create one-to-one between two query types because query type cannot be principal end of a relationship whereas in between one-to-one principal end of a relationship is a must.
As you can see below, the User is able to make a Call, the Operator will log it, writing the time (error on my part, Column2), his own ID and the ID of the caller. The Operator is also able to create a Solution, by generating a Solution ID and describing the solution.
Note that nothing differentiate the User from the Operator in terms of attributes. Indeed they both inherit their ID from the Person entity.
So I have two questions.
First, as you can see, the Call entity has two attributes which are the same column (ID for User and Operator), but will always represent two different people (i.e. a User will never be an Operator). Is this the correct notation for such a thing?
Secondly, I am not sure about having User and Operator as separate entities because no attribute distinguish them from one another, only their ability to do something or not (User can't create a solution). This would mean that they don't have attributes apart from the ones they inherit. Is this correct or should the two entities be merged under the Personentity?
Thanks in advance.
It's valid to create subtypes with distinct relationships and/or constraints, even if they have no distinct attributes. You'll be able to use referential integrity to ensure that Operator IDs and User IDs don't get mixed up in the Call table, and it's possible to enforce mutual exclusion between the IDs in the User and Operator tables.
As far as notation is concerned, I would show the ID in the User and Operator tables, and use Crow's foot lines to represent the FK constraints between the tables. If I wanted to make the subtyping explicit, I would rather show that on an EER diagram using Chen's notation than on a table diagram.
I am currently trying to set up a relational database (H2) that projects an object orientated structure of JAVA Model into the relational tables of my database. I am using the JDBC and H2 RDBMS.
So Here is my problem:
I have an object of type "attribute" that is supposed to be stored in the table "attribute". The owner of this attribute can either be an object of type "Function" or of type "Block" who both have a table on their own. One attribute-object can only be owned by one object (either function or block), making this a 1:n cardinality.
I am however struggling with how to include the owner in the attribute table. If I create a table named "ownerID" and store the ID of the owner (a globally unique ID btw) in it, the Database is missing the information about which table is containing this ID (even though its a GUID).
-Is it okay for example, to include another column containing the name of the table that the owner_ID belongs to ?
-another idea was to include one "functionOwnerID" column and one "blockOwnerID" and leaving one of them empty, but this seems like a rather dirty solution to me.
I hope my description of the problem was clear, and thanks in advance !
best regards,
Moritz
"Is it okay for example, to include another column containing the name of the table that the owner_ID belongs to ?"
That's how polymorphic relationships work! :)
Edit: (yes, you can do that and it's actually pretty common)
References:
(Rails/ActiveRecord Docs): http://guides.rubyonrails.org/association_basics.html#polymorphic-associations
(Laravel/Eloquent Docs): https://laravel.com/docs/5.4/eloquent-relationships#polymorphic-relations
Is is possible to use a Collection such as a Multiset or Array as the foreign key in a database scheme?
Background: A student proposes to use such a construct (don't use a join table for the n:m association) to store the following object structure in a database
public class Person {
String name;
List<Resource> res;
…
}
public class Resource {
int id;
List<Person> prs;
…
}
SQL:2003
IMHO, the student didn't understand relational concepts. I don't know how collection types are implemented in todays databases, but they most probably store them in separate tables.
Edit
If it would be technically possible, I doubt that it would be useful. Consider the query language. Sql is designed for relational structures, I doubt that you could really have the same flexibility and possibilities using collection types. If you had it, you couldn't read it anymore. Consider indexes. etc. etc.
Relational structures are primitive, but very powerful and fast. You can do (almost) everything with them. Collection type are actually not needed, although they may be useful in certain cases. Using collections (for relational stuff) just would be more complex and less pure.
As David pointed out, theory allows attribute values to be of a collection type.
However, in your case, which is just to model n:m relationships (am I right about that), it simply does not apply.
If a Person P1 has associated resources R1 and R2, the row for this person would be like {P1, {R1, R2}}. If that collection-typed column were a foreign key referencing some other table, it would mean that there had to be another table in which a row appeared with the collection value {R1, R2} in some column. Which table would that be in your example ?
Collection-typed attributes are mostly useful if you have a need for dealing with empty collections alongside non-empty ones. There is no relational join in the world that will do its equivalent for you.
Simply put, I would have said no. I don't think that it is possible in SQL2003 and in any case it would couple the code and the database structure too closely. Remember good practice of structuring code so that a change to your database doesn't require a change to your code and vice versa.
As Stefan said you need separate tables for Resource and Person with Foreign Key links to the indexes between them.
So based on the classes shown each table would need 3 coloumns.
You would then obtain your class data by using an appropriate query to the database.
In principle, yes you can implement such a referential constraint. That's assuming your RDBMS allows a suitable type for the set of values. For instance it could be a relation value if relation-valued attributes (RVA) are supported.
If it was a RVA then the constraint could easily be expressed in the relational algebra / calculus or its equivalent. For instance you can do it in a RDBMS like Rel which supports the Tutorial D language. Doing it in SQL is probably going to be a lot harder - but then SQL is not a real relational language.
Of course, the fact that you can do it relationally does not necessarily make it a good idea...
I'm designing this collection of classes and abstract (MustInherit) classes…
This is the database table where I'm going to store all this…
As far as the Microsoft SQL Server database knows, those are all nullable ("Allow Nulls") columns.
But really, that depends on the class stored there: LinkNode, HtmlPageNode, or CodePageNode.
Rules might look like this...
How do I enforce such data integrity rules within my database?
UPDATE: Regarding this single-table design...
I'm still trying to zero in on a final architecture.
I initially started with many small tables with almost zero nullalbe fields.
Which is the best database schema for my navigation?
And I learned about the LINQ to SQL IsDiscriminator property.
What’s the best way to handle one-to-one relationships in SQL?
But then I learned that LINQ to SQL only supports single table inheritance.
Can a LINQ to SQL IsDiscriminator column NOT inherit?
Now I'm trying to handle it with a collection of classes and abstract classes.
Please help me with my .NET abstract classes.
Use CHECK constraints on the table. These allow you to use any kind of boolean logic (including on other values in the table) to allow/reject the data.
From the Books Online site:
You can create a CHECK constraint with
any logical (Boolean) expression that
returns TRUE or FALSE based on the
logical operators. For the previous
example, the logical expression is:
salary >= 15000 AND salary <= 100000.
It looks like you are attempting the Single Table Inheritance pattern, this is a pattern covered by the Object-Relational Structural Patterns section of the book Patterns of Enterprise Application Architecture.
I would recommend the Class Table Inheritance or Concrete Table Inheritance patterns if you wish to enforce data integrity via SQL table constraints.
Though it wouldn't be my first suggestion, you could still use Single Table Inheritance and just enforce the constraints via a Stored Procedure.
You can set up some insert/update triggers. Just check if these fields are null or notnull, and reject insert/update operation if needed. This is a good solution if you want to store all the data in the same table.
You can create also create a unique table for each classes as well.
Have a unique table for each type of node.
Why not just make the class you're building enforce the data integrity for its own type?
EDIT
In that case, you can either a) use logical constraints (see below) or b) stored procedures to do inserts/edits (a good idea regardless) or c) again, just make the class enforce data integrity.
A mixture of C & B would be the course of events I take. I would have unique stored procedures for add/edits for each node type (i.e. Insert_Update_NodeType) as well as make the class perform data validation before saving data.
Personally I always insist on putting data integrity code on the table itself either via a trigger or a check constraint. The reason why is that you cannot guarantee that only the user interface will update insert or delete records. Nor can you guarantee that someone might not write a second sp to get around the constraints in the orginal sp without understanding the actual data integrity rules or even write it because he or she is unaware of the existence of the sp with the rules. Tables are often affected by DTS or SSIS packages, dynamic queries from the user interface or through Query analyzer or the query window, or even by scheduled jobs that run code. If you do not put the data integrity code at the table level, sooner or later your data will not have integrity.
It's probably not the answer you want to hear, but the best way to avoid logical inconsistencies, you really want to look at database normalisation
Stephen's answer is the best. But if you MUST, you could add a check constraint the HtmlOrCode column and the other columns which need to change.
I am not that familiar with SQL Server, but I know with Oracle you can specify Constraints that you could use to do what you are looking for. I am pretty sure you can define constraints in SQL server also though.
EDIT: I found this link that seems to have a lot information, kind of long but may be worth a read.
Enforcing Data Integrity in Databases
Basically, there are four primary types of data integrity: entity, domain, referential and user-defined.
Entity integrity applies at the row level; domain integrity applies at the column level, and referential integrity applies at the table level.
Entity Integrity ensures a table does not have any duplicate rows and is uniquely identified.
Domain Integrity requires that a set of data values fall within a specific range (domain) in order to be valid. In other words, domain integrity defines the permissible entries for a given column by restricting the data type, format, or range of possible values.
Referential Integrity is concerned with keeping the relationships between tables synchronized.
#Zack: You can also check out this blog to read more details about data integrity enforcement, here- https://www.bugraptors.com/what-is-data-integrity/
SQL Server doesn't know anything about your classes. I think that you'll have to enforce this by using a Factory class that constructs/deconstructs all these for you and makes sure that you're passing the right values depending upon the type.
Technically this is not "enforcing the rules in the database" but I don't think that this can be done in a single table. Fields either accept nulls or they don't.
Another idea could be to explore SQL Functions and Stored Procedures that do the same thing. BUt you cannot enforce a field to be NOT NULL for one record and NULL for the next one. That's your Business Layer / Factory job.
Have you tried NHibernate? It's much more matured product than Entity Framework. It's free.