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Search found 1042 results on 42 pages for 'relational calculus'.

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• SQL SELECT: "Give me all documents where all of the documents procedures are 'work in progress'"

  - by prestonmarshall

  This one really has me stumped. I have a documents table which hold info about the documents, and a procedures table, which is kind of like a revisions table for each document. What I need to do is write a select statement which gives me all of the documents where all of the procedures have the status "work_in_progress". Here's an example procedures table: document_id | status 1 | 'wip' 1 | 'wip' 1 | 'wip' 1 | 'approved' 2 | 'wip' 2 | 'wip' 2 | 'wip' Here, I would want my query to only return document id 2, because all of its statuses are work_in_progress. I DO NOT want document_id 1 since one of its statuses is 'approved'. I believe this is relational division I want, but I'm not sure where to start. This is MySQL 5.0 FYI.

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• Suggest Cassandra data model for an existing schema

  - by Andriy Bohdan

  Hello guys! I hope there's someone who can help me suggest a suitable data model to be implemented using nosql database Apache Cassandra. More of than I need it to work under high loads and large amounts of data. Simplified I have 3 types of objects: Product Tag ProductTag Product: key - string key name - string .... - some other fields Tag: key - string key name - unique tag words ProductTag: product_key - foreign key referring to product tag_key - foreign key referring to tag rating - this is rating of tag for this product Each product may have 0 or many tags. Tag may be assigned to 1 or many products. Means relation between products and tags is many-to-many in terms of relational databases. Value of "rating" is updated "very" often. I need to be run the following queries Select objects by keys Select tags for product ordered by rating Select products by tag order by rating Update rating by product_key and tag_key The most important is to make these queries really fast on large amounts of data, considering that rating is constantly updated.

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• AJAX, PHP, XML, and cascading drop-down lists

  - by Dave Jarvis

  What PHP libraries would you recommend to implement the following: Three dependent drop-down lists Three XML data sources AJAX-based Essentially, I'd like to create an XML database and wire up a form that allows the user to select three different dependent parameters: User clicks Region User clicks District (filtered by Region) User clicks Station (filtered by District) Even though I would like to use PHP and XML, the general problem is: One XHTML form Three dependent, cascading drop-down lists Three flat files (no relational database) for the list data The solution must be efficient, simple, reliable, and cross-browser. What technologies would you recommend to solve the problem? Thank you!

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• MDX performance vs. T-SQL

  - by SubPortal

  I have a database containing tables with more than 600 million records and a set of stored procedures that make complex search operations on the database. The performance of the stored procedures is so slow even with suitable indexes on the tables. The design of the database is a normal relational db design. I want to change the database design to be multidimensional and use the MDX queries instead of the traditional T-SQL queries but the question is: Is the MDX query better than the traditional T-SQL query with regard to performance? and if yes, to what extent will that improve the performance of the queries? Thanks for any help.

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• Strategy Design Pattern -- *dynamic* !!!

  - by alexeypro

  My application will have different strategies for my objects. What's the best way of implementing that? I would really love the case when we can make strategy classes implementation dynamically loaded from, say, some relational database. Not sure how do that better, though. What's the best approach? Idea is that say we want to apply to object MyObj strategy Strategy123 then we just load from database by ID 123 the object, deserialize it, get the Strategy class, and use it with MyObj. The maintenance while sounds easier from the first look can be a pain in the long run if Strategy interfaces changes, etc. What can I do also? I want to find solution when I should be keeping Strategy classes in codebase -- just for the sake that I don't need code change and re-deployment of the application if my Strategy changes, or I add new strategy. Please advise!

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• When to use CouchDB vs RDBMS

  - by Andrew Whitehouse

  I am looking at CouchDB, which has a number of appealing features over relational databases including: intuitive REST/HTTP interface easy replication data stored as documents, rather than normalised tables I appreciate that this is not a mature product so should be adopted with caution, but am wondering whether it is actually a viable replacement for an RDBMS (in spite of the intro page saying otherwise - http://couchdb.apache.org/docs/intro.html). Under what circumstances would CouchDB be a better choice of database than an RDBMS (e.g. MySQL), e.g. in terms of scalability, design + development time, reliability and maintenance. Are there still cases where an RDBMS is still clearly the right choice? Is this an either-or choice, or is a hybrid solution more likely to emerge as best practice?

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• large amount of data in many text files - how to process?

  - by Stephen

  Hi, I have large amounts of data (a few terabytes) and accumulating... They are contained in many tab-delimited flat text files (each about 30MB). Most of the task involves reading the data and aggregating (summing/averaging + additional transformations) over observations/rows based on a series of predicate statements, and then saving the output as text, HDF5, or SQLite files, etc. I normally use R for such tasks but I fear this may be a bit large. Some candidate solutions are to 1) write the whole thing in C (or Fortran) 2) import the files (tables) into a relational database directly and then pull off chunks in R or Python (some of the transformations are not amenable for pure SQL solutions) 3) write the whole thing in Python Would (3) be a bad idea? I know you can wrap C routines in Python but in this case since there isn't anything computationally prohibitive (e.g., optimization routines that require many iterative calculations), I think I/O may be as much of a bottleneck as the computation itself. Do you have any recommendations on further considerations or suggestions? Thanks

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• Video learning for database design

  - by donpal

  I'm trying to learn good relational database design (using mysql and php if that makes any difference). I've already done some database work, so I'm not totally clueless, but I suspect that my solutions may not have adhered to best practices for efficient searching, optimization, etc. Can someone suggest a good set of videos on the topic? If you know something is superb or has really made a difference in your own learning, please post your suggestion. Prefer videos, but books (as long as they're not too huge) are ok too. But prefer videos. Thank you

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• Is adding indexes to a SQL Server ever a bad idea?

  - by Aerik

  We have a mid-size SQL Server based application that has no indexes defined. Not even on the the identity columns. I suggested to our moderately expensive application consultant that perhaps we might get better performance (particularly as our database grows) by creating some indexes on appropriate fields, and he said: "Indexes will significantly impact other areas of the application and customers should not create them under any circumstances." Anybody ever heard of anything like this? Are there ever circumstances where one should not create any indexes? I can see nothing special about this app - it's got int identity columns, then lots of string columns, bunch of relational tables but nothing special or weird that I can see. Thanks!

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• Scaffolding Web Services in Grails

  - by Dan

  I need to implement a web app, but instead of using relational database I need to use different SOAP Web Services as a back-end. An important part of application only calls web services and displays the result. Since Web Services are clearly defined in form of Operation: In parameters and Return Type it seems to me that basic GUI could be easily constructed just like in the case of scaffolding based on Domain Entities. For example in case of SearchProducts web service operation I need to enter search parameters as input, so the search page can be constructed. Operation will return a list of products, so I need a page that will display this list in some kind of table. Is there already some library in grails that let you achieve this. If not, how would you go about creating one?

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• Cloned Cached item has memory issues

  - by ioWint

  Hi there, we are having values stored in Cache-Enterprise library Caching Block. The accessors of the cached item, which is a List, modify the values. We didnt want the Cached Items to get affected. Hence first we returned a new List(IEnumerator of the CachedItem) This made sure accessors adding and removing items had little effect on the original Cached item. But we found, all the instances of the List we returned to accessors were ALIVE! Object relational Graph showed a relationship between this list and the EnterpriseLibrary.CacheItem. So we changed the return to be a newly cloned List. For this we used a LINQ say (from item in Data select new DataClass(item) ).ToList() even when you do as above, the ORG shows there is a relationship between this list and the CacheItem. Cant we do anything to create a CLONE of the List item which is present in the Enterprise library cache, which DOESNT have ANY relationship with CACHE?!

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• Core Data vs SQLite 3

  - by Jason Medeiros

  I am already quite familiar with relational databases and have used SQLite (and other databases) in the past. However, Core Data has a certain allure, so I am considering spending some time to learn it for use in my next application. Is there much benefit to using Core Data over SQLite, or vice versa? What are the pros/cons of each? I find it hard to justify the cost of learning Core Data when Apple doesn't use it for many of its flagship applications like Mail.app or iPhoto.app - instead opting for SQLite databases. SQLite is also used extensively on the iPhone. Can those familiar with using both comment on their experience? Perhaps, as with most things, the question is deeper than just using one over the other?

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• Essential skills of a Data Scientist

  - by harshsinghal

  I would like to know more about the relevant skills in the arsenal of a Data Scientist, and with new technologies coming in every day, how one picks and chooses the essentials. A few ideas germane to this discussion: Knowing SQL and the use of a DB such as MySQL, PostgreSQL was great till the advent of NoSql and non-relational databases. MongoDB, CouchDB etc. are becoming popular to work with web-scale data. Knowing a stats tool like R is enough for analysis, but to create applications one may need to add Java, Python, and such others to the list. Data now comes in the form of text, urls, multi-media to name a few, and there are different paradigms associated with their manipulation. What about cluster computing, parallel computing, the cloud, Amazon EC2, Hadoop ? OLS Regression now has Artificial Neural Networks, Random Forests and other relatively exotic machine learning/data mining algos. for company Thoughts?

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• Is there a declarative language for data definitions?

  - by Jekke

  Reading about WPF and thinking about my application's data store at the same time led me to wonder if there are any languages or tools that allow you to define relational data in a declarative way? A shallow Google search suggests no such thing exists. Yet it seems so obviously useful. The kind of tool I have in mind would declaratively describe (at least) entities, relationships and views is a platform-agnostic way that would act as an abstraction layer between data-driven applications and their datastores. Does any such tool exist?

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• Are there any small scale, durable document/object databases?

  - by Joe Doyle

  I have a few .Net projects that would benefit from using a document/object database opposed to a relational one. I think that db4o would be a good choice, but we're not sure how much the cost is. I'd love to use MongoDB but it's design isn't for small scale, single server applications. Are there other options out there that I just haven't run across for small scale applications? EDIT: So is this a space that doesn't have a good solution, yet? Are there no small scale & durable document databases? Would my best choice be to use MongoDB and set the --syncdelay option set to 1?

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• Conditional Join - join 1 tables 2 ways

  - by Jon H

  I have a set of (not very well normalised or relational) tables named PLAN, GROUP, PRODUCT CLIENT Most have linkage i.e. PLAN - CLIENT on clno GROUP to PRODUCT on PRODCD However, the linkage between PLAN and GROUP is tricky. A plan has 2 field of interest GRPNO and PRODCD. What I want to do is if GRPNO != 0 then join GROUP on GRPNO. However if GRPNO = 0 then I want to join GROUP on PRODCD. The frustrating thing is that the fileds I want to return in my queries are the same across the board I just need to be able to vary the join, or join the same table twice. The best I can come up with is 2 queries and merge them using datasets, or possibly using a union. Is there a nifty way to do this in one select? I should point out I am access Foxpro over ODBC to do this. Thank you!

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• Is there a production ready web application framework in Python?

  - by peperg

  I heard lots of good opinions about Python language. They say it's mature, expressive etc... Are there any production-ready web application frameworks in Python. By "production ready" I mean : supports objective-relational mapping with caching and declarative desciption (like JPA, Hibernate etc..) controls oriented user interface support - no HTML templates but something like JSF (RichFaces, Icefaces) or GWT, Vaadin, ZK component decomposition and dependency injection (like EJB or Spring) unit and integration testing good IDE support clustering, modularity etc (like Terracota, OSGi etc..) there are successful applications written in it by companies like IBM, Oracle etc (I mean real business applications not Twitter) could have commercial support Is it possible at all in Python world ? Or only choices are : use Python and write everything from the bottom (too expensice) stick to JEE buy .NET stack

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• NoSql Crash Course/Tutorial

  - by Chris Thompson

  Hi all, I've seen NoSQL pop up quite a bit on SO and I have a solid understanding of why you would use it (from here, Wikipedia, etc). This could be due to the lack of concrete and uniform definition of what it is (more of a paradigm than concrete implementation), but I'm struggling to wrap my head around how I would go about designing a system that would use it or how I would implement it in my system. I'm really stuck in a relational-db mindset thinking of things in terms of tables and joins... At any rate, does anybody know of a crash course/tutorial on a system that would use it (kind of a "hello world" for a NoSQL-based system) or a tutorial that takes an existing "Hello World" app based on SQL and converts it to NoSQL (not necessarily in code, but just a high-level explanation). I see this having one solid answer, but if you guys feel like it should be community wiki, I'll be happy to change it. Thanks! Chris

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• Extracting Demographic and Contact Information from unstructured text files

  - by jn29098

  I am looking to extract specific items out of a large pool of unstructured documents. These documents could be 1-5 pages of text formatted in various ways by the user, but in most cases would contain at least: Name Address (physical) Email Address Phone number website URL I'm looking for a semantic parser that can attempt to extract these elements from the documents so that I can load that information into a relational database and work with these records as contacts. Other services I've looked for, while valuable for other purposes, do not address this specific need. Alchemy API Open Calais Saplo Any thoughts, suggestions or leads?

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• 'e-Commerce' scalable database model

  - by Ruben Trancoso

  I would like to understand database scalability so I've just heard a talk about Habits of Highly Scalable Web Applications http://techportal.ibuildings.com/2010/03/02/habits-of-highly-scalable-web-applications/ On it, the presenter mainly talk about relational database scalability. I also have read something about MapReduce and Column oriented tables, big tables, hypertable etc... trying to understand which are the most up to date methods to scale web application data. But the second group, to me, is being hard to understand where it fits. It serves as transactional, reliable data store? or not, its just for large access and processing and to handle fine graned operations we will ever need to rely on RDBMSs? Could someone give a comprehensive landscape for those new technologies and how to use it?

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• What database works well with 200+GB of data?

  - by taw

  I've been using mysql (with innodb; on Amazon rds) because it's sort of universal default, but it's been ridiculously under-performing, and tweaking it only delays the inevitable. The data is mostly relatively short (<1kB of bytes each) blobs information about 100Ms of urls. There is (or should be, mysql cannot seem to handle it) very high amount of insert / update / retrieve but few complex queries - not that complex queries wouldn't be useful, but because mysql is so slow that it's far faster to get the data out, process it locally, and cache the results somewhere. I can keep tweaking mysql and throwing more hardware at it, but it seems increasingly futile. So what are the options? SQL/relational model/etc. optional - anything will do as long as it's fast, networked, and language-independent.

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• Hierarchical Data in MySQL is fast to retrieve?

  - by ajsie

  i've got a list of all countries - states - cities (- subcities/villages etc) in a XML file and to retrieve for example a state's all cities it's really quick with XML (using xml parser). i wonder, if i put all this information in mysql, is retrieving a state's all cities as fast as with XML? cause XML is designed to store hierarchical data while relational databases like mysql are not. the list contains like 500 000 entities. so i wonder if its as fast as XML using either of: Adjacency list model Nested Set model And which one should i use? Cause (theoretically) there could be unlimited levels under a state. And which is fastest for this huge dataset? Thanks!

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• What are good hosting companies for PHP 5.3 Mysql / CouchDb / MongoDB Dev ( Lithium / CakePHP Framew

  - by Abba Bryant

  I am looking for a quality reliable host for some lithium development. I don't mind a shared platform as long as I have some ssh access. I require php 5.3.x, Mysql 5.x, and the usual imageMagick etc. Non-relational DB support up front would be nice but if they let me set one up myself I would be okay with doing it. I don't need a lot in the way of control panel tools. Good ones are appreciated but bad ones I would prefer not to even deal with. I don't anticipate needing much in the way of email but mail support would be nice to have. Cost isn't a big issue. I don't want to pay an arm and a leg but don't mind paying for what I need. Good support and decent uptime would be nice but I don't need an SLO or anything.

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• Hierarchical Data in MySQL is as fast as XML to retrieve?

  - by ajsie

  i've got a list of all countries - states - cities (- subcities/villages etc) in a XML file and to retrieve for example a state's all cities it's really quick with XML (using xml parser). i wonder, if i put all this information in mysql, is retrieving a state's all cities as fast as with XML? cause XML is designed to store hierarchical data while relational databases like mysql are not. the list contains like 500 000 entities. so i wonder if its as fast as XML using either of: Adjacency list model Nested Set model And which one should i use? Cause (theoretically) there could be unlimited levels under a state (i heard that adjacency isn't good for unlimited child-levels). And which is fastest for this huge dataset? Thanks!

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• Dealing w/ Sqlite Join results in a cursor

  - by Bill

  I have a one-many relationship in my local Sqlite db. Pretty basic stuff. When I do my left outer join I get back results that look like this: the resulting cursor has multiple rows that look like this: A1.id | A1.column1 | A1.column2 | B1.a_id_fk | B1.column1 | B1.column2 A1.id | A1.column1 | A1.column2 | B2.a_id_fk | B2.column1 | B2.column2 and so on... Is there a standard practice or method of dealing with results like this ? Clearly there is only A1, but it has many B-n relationships. I am coming close to using multiple queries instead of the "relational db way". Hopefully I am just not aware of the better way to do things. I intend to expose this query via a content provider and I would hate for all of the consumers to have to write the same aggregation logic.

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