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  • Computer components which have unique ID

    - by user23950
    What are the computer parts that has a unique ID? Be it software or hardware. For example, IP Address. And the MAC ID in the NIC. Unique ID's that could be used by bad sites to distinguish you from the rest of the crowd. Edit: Or anything that cannot be changed. Anything that is embedded in the hardware that cannot be changed.

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  • Rejuvenated: Script Creates and Drops for Candidate Keys and Referencing Foreign Keys

    - by Adam Machanic
    Once upon a time it was 2004, and I wrote what I have to say was a pretty cool little script . (Yes, I know the post is dated 2006, but that's because I dropped the ball and failed to back-date the posts when I moved them over here from my prior blog space.) The impetus for creating this script was (and is) simple: Changing keys can be a painful experience. Sometimes you want to make a clustered key nonclustered, or a nonclustered key clustered. Or maybe you want to add a column to the key. Or remove...(read more)

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  • Working with Temporal Data in SQL Server

    - by Dejan Sarka
    My third Pluralsight course, Working with Temporal Data in SQL Server, is published. I am really proud on the second part of the course, where I discuss optimization of temporal queries. This was a nearly impossible task for decades. First solutions appeared only lately. I present all together six solutions (and one more that is not a solution), and I invented four of them. http://pluralsight.com/training/Courses/TableOfContents/working-with-temporal-data-sql-server

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  • Highly scalable and dynamic "rule-based" applications?

    - by Prof Plum
    For a large enterprise app, everyone knows that being able to adjust to change is one of the most important aspects of design. I use a rule-based approach a lot of the time to deal with changing business logic, with each rule being stored in a DB. This allows for easy changes to be made without diving into nasty details. Now since C# cannot Eval("foo(bar);") this is accomplished by using formatted strings stored in rows that are then processed in JavaScript at runtime. This works fine, however, it is less than elegant, and would not be the most enjoyable for anyone else to pick up on once it becomes legacy. Is there a more elegant solution to this? When you get into thousands of rules that change fairly frequently it becomes a real bear, but this cannot be that uncommon of a problem that someone has not thought of a better way to do this. Any suggestions? Is this current method defensible? What are the alternatives? Edit: Just to clarify, this is a large enterprise app, so no matter which solution works, there will be plenty of people constantly maintaining its rules and data (around 10). Also, The data changes frequently enough to say that some sort of centralized server system is basically a must.

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  • Constraint-based expert systems design and development [on hold]

    - by Alex B.
    I would appreciate some recommendations & resources on design and development of expert systems, in particular, knowledge-based & constraint-based (not recommendation) systems. Ideally, your answers should consider the perspective (context) of using a SaaS business model and open source rules engine. How would you advise to address performance, scalability and other architectural criteria? Any other considerations on undertaking such project will be appreciated. Thanks much in advance!

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  • Representing and executing simple rules - framework or custom?

    - by qtips
    I am creating a system where users will be able to subscribe to events, and get notified when the event has occured. Example of events can be phone call durations and costs, phone data traffic notations, and even stock rate changes. Example of events: customer 13532 completed a call with duration 11:45 min and cost $0.4 stock rate for Google decreased with 0.01% Customers can subscribe to events using some simple rules e.g. When stock rate of Google decreases more than 0.5% When the cost of a call of my subscription is over $1 Now, as the set of different rules is currently predefined, I can easily create a custom implemention that applies rules to an event. But if the set of rules could be much larger, and if we also allow for custom rules (e.g. when stock rate of Google decreses more than 0.5% AND stock rate of Apple increases with 0.5%), the system should be able to adapt. I am therefore thinking of a system that can interpret rules using a simple grammer and then apply them. After som research I found that there exists rule-based engines that can be used, but I am unsure as they seem too complicated and may be a little overkill for my situation. Is there a Java framework suited for this area? Should we use framework, a rule engine, or should we create something custom? What are the pros and cons?

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  • IIS 7: launch unique site instance per host name

    - by OlduwanSteve
    Is it possible to configure IIS 7 so that a single site with multiple bindings (or wildcard bindings) will launch a unique instance for each unique host name? To explain why this is desirable, we have an application that retrieves its configuration from a remote system. The behaviour of the application is governed by this configuration and not by the 'web.config'. The application uses its host name as a key to retrieve the configuration. Currently it is a manual process to create an identical IIS site for each instance of the application, differing only by the bindings. My thought, if it were possible, is that it would be nice to have one IIS site that effectively works as a template for an arbitrary number of dynamic sites. Whenever it is accessed by a unique host name a new instance of the site would be launched, and all further requests to that host name would go to that instance just as though I had created the site by hand. I use IIS regularly, but only for fairly straightforward site hosting. I'd like to know if this could be configured with vanilla IIS 7, but would also welcome answers that require a plugin or 3rd party product. Programming/architectural suggestions about changes to the app wouldn't really be appropriate for serverfault.

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  • Entity Framework - Foreign key constraints not added for inherited entity

    - by Tri Q
    Hello, It appears to me that a strange phenomenon is occurring with inherited entities (TPT) in EF4. I have three entities. 1. Asset 2. Property 3. Activity Property is a derived-type of Asset. Property has many activities (many-to-many) When modeling this in my EDMX, everything seems fine until I try to insert a new Property into the database. If the property does not contain any Activity, it works, but all hell breaks loose when I add some new activities to the new Property. As it turns out after 2 days of crawling the web and fiddling around, I noticed that in the EF store (SSDL) some of the constraints between entities were not picked up during the update process. Property_Activity table which links properties and activities show only one constraint FK_Property_Activity_Activity but FK_Property_Activity_Property was missing. I knew this is an Entity Framework anomoly because when I switched the relationship in the database to: Asset <-- Asset_Activity <-- Activity After an update, all foreign key constraints are picked up and the save is successful, with or without activities in the new property. Is this intended or a bug in EF? How do I get around this problem? Should I abandon inheritance altogether?

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  • Modeling many-to-one with constraints?

    - by Greg Beech
    I'm attempting to create a database model for movie classifications, where each movie could have a single classification from each of one of multiple rating systems (e.g. BBFC, MPAA). This is the current design, with all implied PKs and FKs: TABLE Movie ( MovieId INT ) TABLE ClassificationSystem ( ClassificationSystemId TINYINT ) TABLE Classification ( ClassificationId INT, ClassificationSystemId TINYINT ) TABLE MovieClassification ( MovieId INT, ClassificationId INT, Advice NVARCHAR(250) -- description of why the classification was given ) The problem is with the MovieClassification table whose constraints would allow multiple classifications from the same system, whereas it should ideally only permit either zero or one classifications from a given system. Is there any reasonable way to restructure this so that a movie having exactly zero or one classifications from any given system is enforced by database constraints, given the following requirements? Do not duplicate information that could be looked up (i.e. duplicating ClassificationSystemId in the MovieClassification table is not a good solution because this could get out of sync with the value in the Classification table) Remain extensible to multiple classification systems (i.e. a new classification system does not require any changes to the table structure)? Note also the Advice column - each mapping of a movie to a classification needs to have a textual description of why that classification was given to that movie. Any design would need to support this.

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  • List all foreign key constraints that refer to a particular column in a specific table

    - by Sid
    I would like to see a list of all the tables and columns that refer (either directly or indirectly) a specific column in the 'main' table via a foreign key constraint that has the ON DELETE=CASCADE setting missing. The tricky part is that there would be an indirect relationships buried across up to 5 levels deep. (example: ... great-grandchild- FK3 = grandchild = FK2 = child = FK1 = main table). We need to dig up the leaf tables-columns, not just the very 1st level. The 'good' part about this is that execution speed isn't of concern, it'll be run on a backup copy of the production db to fix any relational issues for the future. I did SELECT * FROM sys.foreign_keys but that gives me the name of the constraint - not the names of the child-parent tables and the columns in the relationship (the juicy bits). Plus the previous designer used short, non-descriptive/random names for the FK constraints, unlike our practice below The way we're adding constraints into SQL Server: ALTER TABLE [dbo].[UserEmailPrefs] WITH CHECK ADD CONSTRAINT [FK_UserEmailPrefs_UserMasterTable_UserId] FOREIGN KEY([UserId]) REFERENCES [dbo].[UserMasterTable] ([UserId]) ON DELETE CASCADE GO ALTER TABLE [dbo].[UserEmailPrefs] CHECK CONSTRAINT [FK_UserEmailPrefs_UserMasterTable_UserId] GO The comments in this SO question inpire this question.

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  • For an ORM supporting data validation, should constraints be enforced in the database as well?

    - by Ramnique Singh
    I have always applied constraints at the database level in addition to my (ActiveRecord) models. But I've been wondering if this is really required? A little background I recently had to unit test a basic automated timestamp generation method for a model. Normally, the test would create an instance of the model and save it without validation. But there are other required fields that aren't nullable at the in the table definition, meaning I cant save the instance even if I skip the ActiveRecord validation. So I'm thinking if I should remove such constraints from the db itself, and let the ORM handle them? Possible advantages if I skip constraints in db, imo - Can modify a validation rule in the model, without having to migrate the database. Can skip validation in testing. Possible disadvantage? If its possible that ORM validation fails or is bypassed, howsoever, the database does not check for constraints. What do you think? EDIT In this case, I'm using the Yii Framework, which generates the model from the database, hence database rules are generated also (though I could always write them post-generation myself too).

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  • How are hash functions like MD5 unique?

    - by Aly
    Im aware that MD5 has had some collisions but this is more of a high level question about hashing functions. If MD5 hashes any arbitrary string into a 32-digit hex value, then according to the Pigeonhole Principle surely this can not be unique as there are more unique arbitrary strings than there are unique 32-digit hex values

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  • Find unique vertices from a 'triangle-soup'

    - by sum1stolemyname
    I am building a CAD-file converter on top of two libraries (Opencascade and DWF Toolkit). However, my question is plattform agnostic: Given: I have generated a mesh as a list of triangular faces form a model constructed through my application. Each Triangle is defined through three vertexes, which consist of three floats (x, y & z coordinate). Since the triangles form a mesh, most of the vertices are shared by more then one triangle. Goal: I need to find the list of unique vertices, and to generate an array of faces consisting of tuples of three indices in this list. What i want to do is this: //step 1: build a list of unique vertices for each triangle for each vertex in triangle if not vertex in listOfVertices Add vertex to listOfVertices //step 2: build a list of faces for each triangle for each vertex in triangle Get Vertex Index From listOfvertices AddToMap(vertex Index, triangle) While I do have an implementation which does this, step1 (the generation of the list of unique vertices) is really slow in the order of O(n!), since each vertex is compared to all vertices already in the list. I thought "Hey, lets build a hashmap of my vertices' components using std::map, that ought to speed things up!", only to find that generating a unique key from three floating point values is not a trivial task. Here, the experts of stackoverflow come into play: I need some kind of hash-function which works on 3 floats, or any other function generating a unique value from a 3d-vertex position.

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  • Making HABTM relationships unique in CakePHP

    - by Andrea
    I have two models, called Book and Tag, which are in a HABTM relationship. I want a couple (book, tag) to be saved only once. In my models I have var $hasAndBelongsToMany = array( 'Tag' => array( 'className' => 'Tag', 'joinTable' => 'books_tags', 'foreignKey' => 'book_id', 'associationForeignKey' => 'tag_id', 'unique' => true ) ); and viceversa, but the Unique flag does not help me; I can still save two times the same couple. How do I do this in CakePHP? Should I declare the couple (book, tag) unique in the database directly, or will this make CakePHP go nuts? Is there a Cakey way to handle this situation? EDIT: I tried making the couple unique with the query (I'm using MySQL) ALTER TABLE books_tags ADD UNIQUE (book_id,tag_id); but this does not work well. When I save more than one tag at a time, everything goes well if all the couples are new. If at least one of the couples is repeated, CakePHP fails to do the whole operation, so it does not save ANY new couple (not even the good ones).

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  • Domain driven design value object, how to ensure a unique value

    - by Darren
    Hi, I am building a questionnaire creator. A questionnaire consists of sections, sections consist of pages and pages consist of questions. Questionnaire is the aggregate root. Sections, pages and questions can have what are called shortcodes which should be unique within a questionnaire (but not unique within the database hence they are not strictly an identity). I intended to make the shortcode a value object and wanted to include the business rule that it should be unique within the questionnaire but I am unsure how to ensure that. My understanding is that the value object should not access the repository or service layer so how does it find out if it is unique? Thanks for any help. Darren

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  • Constraint Satisfaction Problem

    - by Carl Smotricz
    I'm struggling my way through Artificial Intelligence: A Modern Approach in order to alleviate my natural stupidity. In trying to solve some of the exercises, I've come up against the "Who Owns the Zebra" problem, Exercise 5.13 in Chapter 5. This has been a topic here on SO but the responses mostly addressed the question "how would you solve this if you had a free choice of problem solving software available?" I accept that Prolog is a very appropriate programming language for this kind of problem, and there are some fine packages available, e.g. in Python as shown by the top-ranked answer and also standalone. Alas, none of this is helping me "tough it out" in a way as outlined by the book. The book appears to suggest building a set of dual or perhaps global constraints, and then implementing some of the algorithms mentioned to find a solution. I'm having a lot of trouble coming up with a set of constraints suitable for modelling the problem. I'm studying this on my own so I don't have access to a professor or TA to get me over the hump - this is where I'm asking for your help. I see little similarity to the examples in the chapter. I was eager to build dual constraints and started out by creating (the logical equivalent of) 25 variables: nationality1, nationality2, nationality3, ... nationality5, pet1, pet2, pet3, ... pet5, drink1 ... drink5 and so on, where the number was indicative of the house's position. This is fine for building the unary constraints, e.g. The Norwegian lives in the first house: nationality1 = { :norway }. But most of the constraints are a combination of two such variables through a common house number, e.g. The Swede has a dog: nationality[n] = { :sweden } AND pet[n] = { :dog } where n can range from 1 to 5, obviously. Or stated another way: nationality1 = { :sweden } AND pet1 = { :dog } XOR nationality2 = { :sweden } AND pet2 = { :dog } XOR nationality3 = { :sweden } AND pet3 = { :dog } XOR nationality4 = { :sweden } AND pet4 = { :dog } XOR nationality5 = { :sweden } AND pet5 = { :dog } ...which has a decidedly different feel to it than the "list of tuples" advocated by the book: ( X1, X2, X3 = { val1, val2, val3 }, { val4, val5, val6 }, ... ) I'm not looking for a solution per se; I'm looking for a start on how to model this problem in a way that's compatible with the book's approach. Any help appreciated.

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  • Enum type constraints in C#

    - by Taylor L
    What is the reason behind C# not allowing type constraints on Enum's? I'm sure there is a method behind the madness, but I'd like to understand why it's not possible. Below is what I would like to be able to do (in theory). public static T GetEnum<T>(this string description) where T : Enum { ... }

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  • Hibernate + Spring : cascade deletion ignoring non-nullable constraints

    - by E.Benoît
    Hello, I seem to be having one weird problem with some Hibernate data classes. In a very specific case, deleting an object should fail due to existing, non-nullable relations - however it does not. The strangest part is that a few other classes related to the same definition behave appropriately. I'm using HSQLDB 1.8.0.10, Hibernate 3.5.0 (final) and Spring 3.0.2. The Hibernate properties are set so that batch updates are disabled. The class whose instances are being deleted is: @Entity( name = "users.Credentials" ) @Table( name = "credentials" , schema = "users" ) public class Credentials extends ModelBase { private static final long serialVersionUID = 1L; /* Some basic fields here */ /** Administrator credentials, if any */ @OneToOne( mappedBy = "credentials" , fetch = FetchType.LAZY ) public AdminCredentials adminCredentials; /** Active account data */ @OneToOne( mappedBy = "credentials" , fetch = FetchType.LAZY ) public Account activeAccount; /* Some more reverse relations here */ } (ModelBase is a class that simply declares a Long field named "id" as being automatically generated) The Account class, which is one for which constraints work, looks like this: @Entity( name = "users.Account" ) @Table( name = "accounts" , schema = "users" ) public class Account extends ModelBase { private static final long serialVersionUID = 1L; /** Credentials the account is linked to */ @OneToOne( optional = false ) @JoinColumn( name = "credentials_id" , referencedColumnName = "id" , nullable = false , updatable = false ) public Credentials credentials; /* Some more fields here */ } And here is the AdminCredentials class, for which the constraints are ignored. @Entity( name = "admin.Credentials" ) @Table( name = "admin_credentials" , schema = "admin" ) public class AdminCredentials extends ModelBase { private static final long serialVersionUID = 1L; /** Credentials linked with an administrative account */ @OneToOne( optional = false ) @JoinColumn( name = "credentials_id" , referencedColumnName = "id" , nullable = false , updatable = false ) public Credentials credentials; /* Some more fields here */ } The code that attempts to delete the Credentials instances is: try { if ( account.validationKey != null ) { this.hTemplate.delete( account.validationKey ); } this.hTemplate.delete( account.languageSetting ); this.hTemplate.delete( account ); } catch ( DataIntegrityViolationException e ) { return false; } Where hTemplate is a HibernateTemplate instance provided by Spring, its flush mode having been set to EAGER. In the conditions shown above, the deletion will fail if there is an Account instance that refers to the Credentials instance being deleted, which is the expected behaviour. However, an AdminCredentials instance will be ignored, the deletion will succeed, leaving an invalid AdminCredentials instance behind (trying to refresh that instance causes an error because the Credentials instance no longer exists). I have tried moving the AdminCredentials table from the admin DB schema to the users DB schema. Strangely enough, a deletion-related error is then triggered, but not in the deletion code - it is triggered at the next query involving the table, seemingly ignoring the flush mode setting. I've been trying to understand this for hours and I must admit I'm just as clueless now as I was then.

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  • Increment non unique field during SQL insert

    - by phill
    I'm not sure how to word this cause I am a little confused at the moment, so bare with me while I attempt to explain, I have a table with the following fields: OrderLineID, OrderID, OrderLine, and a few other unimportant ones. OrderLineID is the primary key and is always unique(which isn't a problem), OrderID is a foreign key that isn't unique(also not a problem), and OrderLine is a value that is not unique in the table, but should be unique for any OrderIDs that are the same...so if that didn't make sense, perhaps a picture OrderLineID, OrderID, OrderLine 1 1 1 2 1 2 3 1 3 4 2 1 5 2 2 For all OrderIDs there is a unique OrderLine. I am trying to create an insert statement that gets the max OrderLine value for a specific OrderId so I can increment it, but it's not working so well and I could use a little help. What I have right now is below, I build the sql statement in a program and replace OrderID # with an actual value. I am pretty sure the problem is with the nested select statement, and incrementing the result, but I can't find any examples that do this since my google skills are weak apparently.... INSERT INTO tblOrderLine (OrderID, OrderLine) VALUES (<OrderID #>, (SELECT MAX(OrderLine) FROM tblOrderLine WHERE orderID = <same OrderID #>)+1) any help would be nice.

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  • Wordpress loop > unique loop renders slightly wrong results...

    - by Travis Neilson
    A few things to understand before my question will make sense: I use a hidden category called 'Unique' to specify if the post will use the single.php or a special one used for the unique ones. I want the index to act as a single: showing only one post, displaying next/prev post links, and comments also. I need the index.php to say if the post is in category 15 (unique) than <the_unique_content>, else; <the_default_content> My loop does all this, but the problem is that if the current post is unique, it also displays 1 additional post below the unique post. Here is the loop <?php $wp_query->is_single = true; ?> <?php $post_count = 0; ?> <?php if (have_posts()) : while (have_posts()) : the_post(); ?> <?php if ($post_count == 0) : ?> <?php if (in_category('15')) { ?> <?php the_content(); ?> <?php } else { ?> <?php the_content(); ?> <?php $post_count++; ?> Thanks for any help!

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  • Oracle Unique Indexes

    - by Melvin
    I was creating a new table today in 10g when I noticed an interesting behavior. Here is an example of what I did: CREATE TABLE test_table ( field_1 INTEGER PRIMARY KEY ); Oracle will by default, create a non-null unique index for the primary key. I double checked this. After a quick check, I find a unique index name SYS_C0065645. Everything is working as expected so far. Now I did this: CREATE TABLE test_table ( field_1 INTEGER, CONSTRAINT pk_test_table PRIMARY KEY (field_1) USING INDEX (CREATE INDEX idx_test_table_00 ON test_table (field_1))); After describing my newly created index idx_test_table_00, I see that it is non-unique. I tried to insert duplicate data into the table and was stopped by the primary key constraint, proving that the functionality has not been affected. It seems strange to me that Oracle would allow a non-unique index to be used for a primary key constraint. Why is this allowed?

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  • Add foreign key constraints to existing tables in Ruby on Rails (MySQL)

    - by randombits
    What's the best way to add foreign keys to my existing tables in Rails with an underlying MySQL database? clearly the solution should be done in a migration, as I want this versioned. Otherwise I'd create the constraints myself. I can't seem to find one, conducive response to they above. Again, the tables have already been created with previous migrations. I'm just going back now and adding referential integrity wherever it's applicable.

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