> | ~ } {$ ( The relationship name is always expressed in the parent-to-child direction, such that a sentence can be formed by combining the parent entity name, relationship name, cardinality expression, and child entity name. Retailing in the 21st century is as much about managing information as it is about managing cash, merchandise, customers, stores, vendors and other "real world" business assets. Data model diagrams are refined into three different levels of detail: Entity-relationship, the least detailed level. )
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However, the role names may be used in the category entities. The creation of domains can also be used to define constraints that values assigned to an attribute assigned to a domain. 7 g 7 f | Identifying Relationships Relationships can be discovered by:
interviews with users
joint facilitated sessions
examining business documents
analyzing events $ $ _ $ _ This is called a controlled vocabulary and it is a key value-adding feature of data modeling.
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IDEF1X provides a full set of semantic modeling capabilities wh
A relationship is a type of attribute pointing to an entity instead of a data type. The Sample Entity, Attribute and Simple Relationship diagram shows a NON-IDENTIFYING relationship between Item and Brand. Z T g g ? ? 4 l $ l Entities introduced to resolve non-specific relationships are sometimes called "intersection" or "associative" entities. Rules are no longer shown on the diagrams. For example, although an existence-dependency relationship may exist between the entities BUYER and PURCHASE-ORDER, purchase orders may be uniquely identified by a purchase order number without identifying the associated buyer. C d) 0 )
H Abbreviations and acronyms are permitted; however, the entity name must be meaningful and consistent throughout the model. The second way parent and child entity types may be related is through a non-identifying relationship. @ 33 @ @ @ s f 4 A "complete categorization relationship" is a relationship between two or more entities, in which each instance of one entity, referred to as the generic entity, is associated with exactly one instance of one and only one of the other entities, referred to as category entities. ___ f 3 f
, ( This is illustrated in the next diagram. The Sarbanes Oxley Act of 2002 mandates detailed reporting and tracking of business operational and financial controls. l ( C $)
eric entity and SALARIED-EMPLOYEE and HOURLY-EMPLOYEE are category entities. Business rules or entity relationships that are written descriptions of the manner in which data relates to other data. The diagram below illustrates the assignment of a definition to the ItemID attribute of Item. ( IDEF1X models are also being used to automatically generate database designs and data integrity control logic. S j) 0 `
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H The business and technical meta data for these systems data constitute an information architecture that can both guide the development of internal controls and give corporate principals the confidence that the reports they sign are valid. The RetailTransactionLineItem entity type may be extended in ways that make it a SaleReturnLineItem to capture item sales data, a DiscountLineItem to capture discount data for a retail transaction, a TaxLineItem to capture tax data or a TenderLineItem to capture payment data. ` )
T Click to edit Master title style ! However, if the entity is a child entity in any identifying relationship, it is always shown as a identifier-dependent entity with rounded comers, regardless of its role in the other relationshi
In an entity diagram, an identifying relationship is signified by a solid line between the parent and child entity types. For this example subtype child entity types efficiently represent a retail transaction and the different kinds of line items needed to capture item, discount, tax and tender data. ( , c ( ___ f 3 f
p ( U , U , 8 `T , 8 `T q 0 a 2 This non-specific relationship can be replaced with specific relationships later on in the model development by introducing a third entity, such as PROJECT-ASSIGNMENT, which is a common child entity in specific connection relationships with the EMPLOYEE and PROJECT entities. ( , C ) 0
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5 order 2 ( In the previous example, the discriminator might be named EMPLOYEE-TYPE. ___ f 3 f
0 ( Selecting (by clicking on the box) an entity on a diagram will bring up the entity dictionary.
See Figure 4-4.
It also illustrates how foreign keys and cardinality are presented in an entity diagram. The data model (particularly a third normal form relational model) reduces this risk by insisting on a consistent representation of each data element in a single place in the data model. ps. ? If the circle has a double underline, it indicates that the set of category entities is complete. )
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Category Entities will always be Identifier-Dependent Entities. 8 l A relationship identifies, names and defines an association between two entity types. In a relational data model, an attribute cannot exist independently from an entity type. On diagrams, entity names appear in upper cases with spaces instead of underscores between the words. For example, an EMPLOYEE can be a SALARIED-EMPLOYEE. A non-specific relationship is named in both directions. C BU C EN G
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HZ ID Q D ? : T h) g g ? is going to pay for it. C ) 0 )
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l Relationships incorporate an additional property between parent and child entity types called cardinality. Retailers without a consistent way of identifying, naming and defining entities, attributes and relationships spend a lot of time and money trying to reconcile conflicting summary reports. 0 h ? A non-specific relationship, also referred to as a "many to many relationship", is an association between two entities in which each instance of the first entity is associated with zero, one, or many instances of the second entity and each instance of the second entity is associated with zero, one, or many instances of the first entity.
T Click to edit Master title style ! In addition to cardinality, there is a special type of relationship called a subtype that allows several child entity types to inherit a common parent entity type characteristics. A categorization relationship is shown as a line extending from the generic entity to a circle which is underlined. `
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@ @ @ @ @ @ ys[~TiR$`5!~yu1v8$5;jj;V7m'j}[XtJ:ge;yw4mg1cLj(.Js[355Zr(., 4#i6i#yuD{,?v)t)=,HCQ/+Jq;?0 @(HK/M|`r{u9GkX:j.4#,v6&Jq/I{>l(b;vGyv[A6B>rI'?fY=2qF2O B:tLG,Q\X|77l}?F+liJy5qnN=K_.^p?VppdzCw9%M^e]3um&*T'ZgTA @ E~vj$e. A set of graphic diagrams representing real or abstract objects, their characteristics or attributes, and their relationship to one another.
All of these regimes require retailers to inventory and understand their data assets. Definitions should be expressed in business terms and reflect the business concepts represented by a data model entity, attribute, relationship, domain and other model objects. Associated with each line are verb phrases which define the relationship between the two entities. l Data models are a prerequisite to operating a retail enterprise in today's business climate. Payment Card Industry (PCI) compliance which imposes procedures retailers must implement to protect credit card accounts of their customers requires retailers to map and understand the kinds of data they collect. Data movement-related regulatory information is partially satisfied in the ARTS ODM V7.0/7.1 to ARTS DWM V3.0 extract, transform and load mapping. Data representation defines a data type such as integer, string, floating point, date, time or other standard data type or an extended definition that assigns custom properties and constraints to a base data type. The entity types associated through a relationship fulfill two roles: One entity is a parent entity. U , U , 8 `T , 8 `T 0 2 ips would specify that an employee has zero, one, or more project assignments and that a project has zero, one or more project assignments. T ) 1 ? From a relational database point of view this means that the inherited attribute may be null -- that is point to nothing. In some companies middle and senior managers spend an inordinate amount of time manually reconciling inconsistently defined data. $ C d)
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l For example an Item entity type will have an ItemID attribute to unique identify it. | ile maintaining the "economy of concepts" associated with basic E-R modeling. U 8 U 8 D `T 8 D `T
2 Describing attributes _ Attribute name
Alias(s)
Definition
Existence constraints - what other data is this attribute dependent on
Business rules - business policy that defines one or more assertions that represent constraints. IDEF1X models define data in a fully normalized structure, which allows an initial model to be extended without altering the initial set of entities, relationships, and attributes. If the terminating end of a relationship has a "crow's foot," an instance of the originating entity can be related to one or more instances of the terminating entity.
A glossary that defines the entities and attributes used in the diagrams. ___ f 3 f
$ ( E LA E Class relationships are shown by the subtype entities being drawn inside the supertype entity, as illustrated by the diagram above. IDEF1X semantic constructs are formally defined mathematically (using both set theory and first order logic) based on extensions to the relational theory work of Dr. Ted Codd and the entity-relationship modeling work of Dr. Peter Chen. T 1 ? May dictate the business conditions under which a relationship is created, modified ot deleted. Each entity type has a unique, singular noun phrase assigned as its name. Figure 96 - Sample Entity, Attribute and Simple Relationship. p o t j r The generic entity is independent unless its identifier is inherited through some other relationship. ` g g ? Y May dictate the business conditions under which a relationship is created, modified ot deleted. As modeled here, a RetailTransaction may have zero, one or many RetailTransactionLineItem entity instances associated with it. It will have a Description attribute, etc. See Figure 4-3. The connection relationship may be further defined by specifying the cardinality of the relationship. The default child cardinality is zero, one, or many. Data models are a prerequisite to navigating the complex regulatory reporting environment retailers work in today. C D)
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l Within IDEF1X, the following relationship cardinalities can be expressed: If an instance of the child entity is identified by its association with the parent entity, then the relationship is referred to as an "identifying relationship". ( That is, an instance of the generic entity can correspond to the instance of only one category entity. This same issue comes up when developing reports.
That is, the associated project must be known in order to uniquely identify one task from all other tasks. In a relational data model, each entity type instance is uniquely identified by a primary key. Accordingly all attributes are always identified and shown as part of entity types. That detailed tracking requires that retailers understand how data is organized, populated, stored and protected. In an entity diagram an attribute name that is a foreign key is designated with a "(FK)" suffix. Relationship names are represented as verb phrases. Logical models, in addition to identifying entities, attributes, relationships and domains define what each instance of these object means. Each project assignment is for exactly one employee and exactly one project. @
( A non-specific relationship is depicted as a line drawn between the two associated entities with a dot at each end of the line. Category entities for a generic entity are always mutually exclusive. The operational and decision support systems are based on data being collected and stored in data structures such as tables and files, and then transformed and moved to become knowledge in reports that are signed by corporate principals. d d @ , | ? "
T ) 1 ? Business rules The policies by which an enterprise runs the business
often designate constraints on the data used within the enterprise
can be fount while developing the E-R data model:
in entities
relationships
attributes
domains ( - - Data Normalization V Normalization is a formal technique to develop a highly structured data model
By using three basic normalization steps we:
elimination of data redundancy
structuring of the data for ease of maintenance and modification, done by reducing the anomalies involved with creation, updating and deletion of data
end up with a more stable data model
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First Normal Form All attributes of an entity must have exactly one single occurrence in each instance
a schema whose attributes are all single valued
First Normal form (cont) 2 $ 0 h ?
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l > se direction. For example, the relationship between taxation, merchandise and retailer provided services is explicitly represented in the way items, taxes, tax authorities, retail transactions, inventory control documents, etc. nQ 0 h ? ` j) g g ? This is because the broad retail framework is well established and it is in a stage of development where it is being extended and enhanced not created from scratch. A "P" (for positive) is placed beside the dot to indicate a cardinality of one or more. For example, ARTS has an IdentityGTIN domain type defined as: An identifier for item at POS - Global Trade Item Number (GTIN) is defined by UCC/EAN.
A * That means that the child entity type's existence is dependent on its parent entity type's existence. % Database Design Dick Steflik Entity-Relationship Diagrams 2 E n t i t y - a n y o b j e c t o r t h i n g t h a t i s o f i n t e r e s t t o t h e o r g a n i z a t i o n a n d f o r w h i c h d a t a m u s t b e s t o r e d
A t t r i b u t e - a d e s c r i p t i v e e l e m e n t , u s e d t o c h a r a c t e r i z e a n e n t i t y o r a r e l a t i o n s h i p . Attributes are the most atomic parts of a data model. Data models that establish an enterprise-wide controlled vocabulary eliminate one of the root causes of data inconsistency. A small circle indicates the relationship is optional for the connecting entity, meaning that an instance of the originating entity does not have to satisfy that relationship. An IDEF1X model of a conceptual schema can be easily subsetted and formally mapped through relational algebra to both external and internal schema. p F 0 Each parent entity instance can have none or at most one associated child instance.
The Child Entity in a non-identifying relationship will be an Identifier-Independent Entity unless the entity is also a Child Entity in some Identifying Relationship. The noun phrase is singular, not plural. R e l a t i o n s h i p - d e s c r i b e t h e w a y t h a t e n t i t i e s i n t e r a c t w i t h e a c h o t h e r , a l o n g w i t h t h e b u s i n e s s c o n d i t i o n s u n d e r w h i c h t h e a s s o c i a t e w i t h o n e a n o t h e r . The U.S. Air Force IISS and IDS projects have successfully demonstrated the use of IDEF1X mo
The ARTS Operational Data Model, in technical terms, is a relational data model built using entity relationship modeling notation. Cardinality is not specified for the category entity since it is always zero or one. The relationship names are expressed as a verb phrase (a verb with optional adverbs and prepositions) placed beside the relationship line and separated by a slash, "/". Data models are not just for information technologists. These cardinalities are illustrated in the diagram below.
( # ( Z 4h) g g ? Domains enable retail-specific data types to be derived from SQL base data types. One type of assertion may specify a Boolean constraint between two or more relationships. If the complete set of categories is referenced, the relationship may be read as "must be." , l , 0 h ? ___ f 3 f
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A retail transaction definition is shown in the yellow block. The result of applying the IDEF1X modeling technique is a specification of data meanings and rules typically represented by the following: In key-based and fully attributed models, a distinction is made between two types of entities. The data model by defining each entity type clarifies what each term means. A relationship verb phrases may be established for both directions of a relation between two entities. While focused on payment-related account identification, PCI compliance is pointing the way for further controls on customer identification and personal data. If the cardinality is an exact number, a positive integer number is placed beside the dot. The attribute shared from a parent to a child entity type is called a foreign key.
A verb phrase of "void" indicates that the relationship, through drawn on the diagram, does not exist in the dictionary. p F q 0 a Category entities are also always identifier-dependent. Conversely a child entity type cannot be inserted until the parent it references is inserted. Domain - set of values which the attribute can take on
Format - characterization (ex, text, date, time, money.media)
Length - number of characters or digits
Default value - initial value when first instantiated
Derivation algorithm - for derived attributes, the algorithm that is used to derive the attribute ` ` ? U 8 U 8 D `T 8 D `T
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A path assertion might state that "employees may only be assigned to projects which belong to the same department for which they work". (Also, see Foreign Keys Semantics). The entity name is a noun phrase (a noun with optional adjectives and prepositions) that describe the set of things the entity represents. Each parent entity instance may have zero, one or more associated child entity instances. @ n ? " ! Data modeling provides a formal set of tools and procedures to make information useful. Each parent entity instance is associated with some exact number of child entity instances. Identifying Attributes _ Interviews with users
joint facilitated sessions
Examining various business or system documents ` `
Naming attributes Each attribute of an entity should be uniquely identified
names should always be singular
a good practice is to always precede the attribute name with the entity name
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) g g 1 ? Separate lines extend from the underlined circle to each of the category entities. The definitions supply the semantic content for a data model. If the entity is identifier-dependent then the corners of the box are rounded. G/* d 6 ? U 9 U 9 E `T 9 E `T
" An entity is "identifier-independent" or simply "independent" if each instance of the entity can be uniquely identified without determining its relationship to another entity. The relationship is read as "is a/an" from the rever