Does InterSystems IRIS support one-to-one relationships in the object model?
I referred to the documentation, but it says only something about one-to-many and parent-child relationship types.
Yes! But it is not explicitly mentioned in the documentation.
See this reply for details and a simple example.
Related
I am not that much good at database diagraming. Whenever I am asked to create an ERR Diagram, I use MySQL WorkBench software.
However today I ended up in a conclusion when I see different types of ER Diagrams. My diagrams (designed via MySQL WorkBench) are like below.
And I saw other types of ER Diagrams like below.
Can someone please confirm which ER Diagram model should I use?
An Entity Relationship Diagram is an example of a presentation of a Conceptual Model. A Conceptual Model is used to help people understand the subject area(s) the model represents. Therefore, the correct presentation of a Conceptual Model - which may be or include an Entity Relationship Diagram - is one that all interested parties are satisfied adequately explains these subject areas.
These interested parties should include potential users of a system that incorporates the subject areas, managers of these areas and IT professionals who will be designing and building a system covering these areas.
The agreed Conceptual Model is then taken by the IT professionals and formalized into a Logical Model, which may be presented as a Relational Data Model.
Actually both of them are ER diagrams. However, the second one is its scientific representation. MySQL use a representation which is more understandable way of it.
I'm drawing an ERD for a database and want to know if you need to include the supertypes and sub-types in the ERD. If yes, how to represent it. Thanks.
google for "ER Specialization". This is the term used in ER literature for subtyping. You should get some ways to diagram it, using the "Is-a" triangle connector. Some tutorials place it in "Extended ER features".
Would like to find low-cost relational modeling tools that will allow me to map a logical model in third normal form to a physical model based on EAV. Got any pointers?
EAV fails to conform to rules of relational normalization, therefore there can be no relational modeling tools that support it.
If your model is in 3NF, then there's no reason to model it in EAV. Keep it in 3NF.
I am looking for nosql key value stores that also provide for storing/maintaining relationships between stored entities. I know Google App Engine's datastore allows for owned and unowned relationships between entities. Does any of the popular nosql store's provide something similar?
Even though most of them are schema less, are there methods to appropriate relationships onto a key value store?
It belongs to the core features of graph databases to provide support for relationships between entities. Typically, you model your entities as nodes and the relationships as relationships/edges in the graph. Unlike RDBMS you don't have to define relationships in advance -- just add them to the graph as needed (schema-free). I created a domain modeling gallery giving a few examples of how this can look in practice. The examples use the Neo4j graphdb, a project I'm involved in. The mailing list of this project use to prove very helpful for graph modeling questions.
The document-oriented database Riak has support for links between documents.
You can add support for relationships on top of any database engine (like key/value), but it doesn't come whithout work. It all comes down to your use case. If you provide more details it's easier to come up with a useful answer.
Oops, now I saw that the title says "nosql store" and then your actual question narrows this down to "nosql key value store". As key/value stores have no semantics for defining relationships between entities I'll still post my answer.
MongoDB is a document database, not a key/value store. It does provide, however, a simple form of inter-document references. These work more-or-less like SQL foreign keys that are automatically nulled when the referenced object is deleted.
This is adequate for the same sorts of things for which you'd use foreign keys, but it isn't optimized for serious graph traversal.
The relationships in the Google App Engine are only keys to entities that are automatically de-referenced when accessed in code. And are only values when used to filter against. Its a function of the DB Api rather than anything explicit, so the access to the ReferenceProperty will simply perform a query against the referenced model to get access to the object.
If you look at something like MongoDB, the relationships are stored in-object (from what I remeber), but they can also be stored however you want in the sense that you would create an API that would search the joined table for your item in the relationship in a similar manner to who the App Engine works.
Paul.
I have a many-to-many relationship in my database of objects A to B. When i create a domain service the metadata looks fine. A has a collections of Bs, B has a collection of As. So it is correct. However the *.g.cs file generated doesn't have the same relationship.
Is there a way to make it work? I googled some answer to actually generate objects for the association table but i am curious if i can avoid this.
Thanks
In the current release/version of RIA Services, you'll need the association table. We will most definitely be looking into this of course for a future release.
That said, I think often many-to-many relationships often have some interesting data associated with the relationship and as such, the middle table often has a real use, rather than existing for the sake of existing.
Till MS implements it in RIA, you can use http://m2m4ria.codeplex.com/
We have used in one of our Silverlight/RIA projects for User/Role (many-to-many) relationship and worked fine.