I know there is a way to read avro record into schema compatible with one used to write that record (given both schemas). I wonder whether there is a way to transform record to the similar record with another (but compatible with old one) schema. Compatibility is meant in sense of as it is described here.
Related
I am new to semantic-web and ontology. From few weeks ago I am start reading papers and online course about it. I have an idea to use ontology rule-based system for extending the feature on my existing reminder system, as can be seen in the attached picture. I've read about Ontology, Rules (e.g. SPIN, SPARQL), Inference engine (e.g. Jena), RDF, RDFS, OWL etc. I think I've got the general idea about it.
System Architecture:
However, one thing that I still miss is: how to integrate this rule-based system into my current system. the current system data is stored in RDBMS (mysql) database. Every transaction data on the system has the possibility to be modified in later time after creation. Meanwhile, ontology-based system - AFAIK, rely on RDF data format. My thinking is, there should be a way to convert the trx data from RDBMS to RDF to be ready to use by the ontology system.
My question are:
Does my thinking correct?
What is best practise of this process?
When there is a modified data on the existing record (RDBMS), how to reflect it on the RDF?
In relation to #3, in case of not using RDBMS, how the ontology system manage their RDF data if there is an update of individual property? is that depend on the underlying triple-store database? Since I read that using TDB only able to insert or delete.
Hive supports ACID property only for ORC formatted tables.
Can anyone please let me know the reason or any guide available ?
It's the current limitation, Here's the text from official documentation:
Only ORC file format is supported in this first release. The feature has been built such that transactions can be used by any storage format that can determine how updates or deletes apply to base records (basically, that has an explicit or implicit row id), but so far the integration work has only been done for ORC.
More details about Hive transactions can be found here
There is no specific reason per say.
More formats will be supported in later versions. ORC was the first one to be supported.
https://cwiki.apache.org/confluence/display/Hive/Hive+Transactions
With the load data option that Liquibase provides, one can specify seed data in a CSV format. Is there a way I can provide say, a JSON or XML file with data that Liquibase would understand?
The use case is we are trying to put in some sample data which is hierarchical. E.g. Category - Subcategory relation which would require putting in parent id for all related categories. If there is a way to avoid including the ids in the seed data via say, JSON.
{
"MainCat1": ["SubCat11", "SubCat12"],
"MainCat2": ["SubCat21", "SubCat22"]
}
Very likely to have this as not supported (couldn't make Google help me) but is there a way to write a plugin or something that does this? Pointer to a guide (if any) would help.
NOTE: This is not about specifying the change log in that format.
This not currently supported and supporting it robustly would be pretty difficult. The main difficultly lies in the fact that Liquibase is designed to be database-platform agnostic, combined with the design goal of being able to generate the SQL required to do an operation without actually doing the operation live.
Inserting data like you want without knowing the keys and just generating SQL that could be run later is going to be very difficult, perhaps even impossible. I would suggest approaching Nathan, who is the main developer for Liquibase, more directly. The best way to do that might be through the JIRA bug database for Liquibase.
If you want to have a crack at implementing it, you could start by looking at the code for the LoadDataChange class (source in Github), which is where the CSV support currently lives.
I inherit a project of a program that configures devices via ethernet. Settings are stored in the database. The set of settings is constantly changing as devices are developing so there's a need for a simple schema change (user must be able to perform this operation).
Now, this simplicity is achieved by the XSD-scheme (easy readable and editable), and the data is stored as XML. This approach also satisfies the requirement of the use of various database engines (MS SQL and Oracle are currently supported).
I want to move database structure to the relational model. Are there any solutions which are as easy-to-change as described one while using a relational database?
I want to move database structure to the relational model.
Why?
Do you want to be able to index/query parts of the configuration, or be able to change just one part of the configuration without touching the rest?
If no, then just treating the XML as opaque BLOB should be sufficient.
If yes, then you'll have to tell us more about the actual structure of configuration.1
1 BTW, some DBMSes can "see inside" the XML, index the elemnts and so on, but that would no longer be DBMS-agnostic.
There are several solutions to your design problem.
I suggest the following;
Use a different database. Relational databases are not the best choice for this kind of data. There are databases with good support for dynamic data. One example of such a database is mongoDB, which uses JSON-style documents.
or
2. Create one (or a small set) of Key/Value table(s). You can support a hierarcical structure by adding a parent column that points to the parent key-value pair.
I wouldn't recommend changing a relational db schema on the fly as the result of a user operation. It goes against fundamental design rules for relational database design.
This question is in continuation to my previous question related to File I/O.
I am using RFile to open a file and read/write data to it. Now, my requirement is such that I would have to modify certain fields within the file. I separate each field within a record with a colon and each record with a newline. Sample is below:
abc#def.com:Albert:1:2
def#ghi.com:Alice:3:1
Suppose I want to replace the '3' in the second record by '2'. I am finding it difficult to overwrite specific field in the file using RFile because RFile does not provide its users with such facility.
Due to this, to modify a record I have to delete the contents of the file and serialize ( that is loop through in memory representation of records and write to the file ). Doing this everytime there is a change in a record's value is quite expensive as there are hundreds of records and the change could be quite frequent.
I searched around for alternatives and found CPermanentFileStore. But I feel the API is hard to use as I am not able to find any source on the Internet that demonstrates its use.
Is there a way around this. Please help.
Depending on which version(s) of Symbian OS you are targetting, you could store the information in a relational database. Since v9.4, Symbian OS includes an SQL implementation (based on the open source SQLite engine).
Using normal files for this type of records takes a lot of effort no matter the operating system. To be able to do this efficiently you need to reserve space in the file for expansion of each record - otherwise you need to rewrite the entire file if a record value changes from say 9 to 10. Also storing a lookup table in the file will make it possible to jump directly to a record using RFile::Seek.
The CPermamanentFileStore simplifies the actual reading and writing of the file but basically does what you have to do yourself otherwise. A database may be a better choice in this instance. If you don't want to use a database I think using stores would be be a better solution.