Install i-refactory modeller

2023-04-17

In this section we will guide you through the installation of the i-refactory modeller.

Supported Power Designer Releases

Sybase PowerDesigner version 16.5 SP3 PL03 is supported, which means that we have tested the combination of Sybase Power Designer in combination with our extensions and can guarantee that there are no technical conflicts or usage issues.

This install instruction guides you through installing PowerDesigner and configuring PowerDesigner.

{tip} It is important to carefully follow the installation instructions in the following sections.

Step 1. Install SAP PowerDesigner

First, you need to get a valid license of SAP PowerDesigner Data Modeller, release 16.5 SP03 PL03. Then, follow the install instructions of SAP PowerDesigner.

When installing SAP PowerDesigner Data Modeller you should at least select the following components:

Install the required PowerDesigner components
Install the required PowerDesigner components

Step 2. Unpack the i-refactory modeller add-ons

The i-refactory modeller add-ons are shipped as a zip-file., which contains the following folders:

  • i-refactory-modeller
    • dbms
    • extensions
    • model-templates
    • models
    • settings-sets

You should unzip the content to your HOME folder or to a shared folder on your local machine. We will refer to this install folder in the next paragraphs as I-REFACTORY-MODELLER-PATH.

{info} Remember the folder where you have copied the i-refactory modeller add-ons, as you will need this location later.

Step 3. Change General Options

PowerDesigner pre-ships with some default settings in General Options. In the following, we show how some of these default settings should be changed.

  1. Open the General Settings as shown in the figure below.

    PowerDesigner General Options
    PowerDesigner General Options

  2. Change the General settings.

    PowerDesigner change general settings in general options
    PowerDesigner change general settings in general options

  3. Change the Dialog settings.

    PowerDesigner change dialog settings in general options
    PowerDesigner change dialog settings in general options

  4. Create Variables.

    When we export the DDL and metadata, we need a default path where we should create the results of the export. Create a variable with the name as shown in the figure below and assign a valid path value. In the figure below we set the value to "C:\temp".

    PowerDesigner create a variable for the default export path
    PowerDesigner create a variable for the default export path

  5. Create Named Paths.

    Each time when PowerDesigner saves your models as .pdm files, it saves the filepath of any referenced files or models. For example, the extension files used, shortcuts to other models, etcetera.

    If someone else — on a different computer — opens your models, this might result in references to files that cannot be found on that computer. By creating named path variables PowerDesigner replaces the string as set in Path with the name of the named path variable. This reduces the issues of not being able to find these files.

    To enable this capability of PowerDesigner, you need to create two named path variables exactly as shown in the two selected rows in the figure below.

    PowerDesigner create named path variables
    PowerDesigner create named path variables

    The value for the named path variable _IREFACTORY_MANAGEMENT_MODEL should be set to I-REFACTORY-MODELLER-PATH\models.

    The value for the named path variable _IREFACTORY_RESOURCES should be set to I-REFACTORY-MODELLER-PATH.

    {info} Create the named path variables exactly as shown, beginning with an underscore and in capitals.

  6. Configure Model Creation.

    The i-refactory modeller add-ons contain default templates for the various models you can create. These templates have pre-configured settings. For example, the proper attachments of required extensions.

    To enable model creation with templates, you need to configure the path to these model templates and enable its usage.

    PowerDesigner model creation
    PowerDesigner model creation

    Set the path value to I-REFACTORY-MODELLER-PATH\model_templates.

Step 4. Configure DBMS resources

PowerDesigner needs to be aware of the filepath of custom resources. As the i-refactory modeller add-ons contain custom resources for the DBMS, we need to configure the filepath for these resources.

  1. Open the menu to change the settings for the DBMS resource.

    Create a path to the custom DBMS extensions
    Create a path to the custom DBMS extensions

  2. Click the path icon in the window shown.

    Open the path window
    Open the path window

  3. Next, you will need to add an additional directory. You can do so by clicking the add icon.

    Add a directory
    Add a directory

    This opens a browser to your local file system. Select the directory I-REFACTORY-MODELLER-PATH\dbms. A new directory is now added to the list of directories.

  4. Make sure the new added directory is on top of the list by clicking the move-up button.

    Move the directory to the top of the list
    Move the directory to the top of the list

  5. You have finished adding the DBMS resources and you should now have a configuration as shown in the figure below.

    Result of adding the DBMS resources
    Result of adding the DBMS resources

Step 5. Configure Physical Data Model resources

  1. Open the menu to change the settings for the Physical Data Model resources.

    Change Physical Model Resource settings
    Change Physical Model Resource settings

  2. Click the path icon in the window shown.

  3. Next, you will need to add an additional directory. You can do so by clicking the add icon.

    Select the directory I-REFACTORY-MODELLER-PATH\extensions from the file system browser. A new directory is now added to the list of directories.

  4. Make sure the new added directory is on top of the list by clicking the move-up button.

  5. You have finished adding the Physical Data Model resources and you should now have a configuration as shown in the figure below.

    Result of adding Physical Data Model resources
    Result of adding Physical Data Model resources

Step 6. Configure DBMS and Settings Sets

When you create a physical data model in PowerDesigner you can choose the DBMS for which you are creating the physical data model.

We need to set the default DBMS to SQL Server.

  1. First create a new physical diagram

    Menu > File > New Model > Model Types > New Physical Model > Physical Diagram.

  2. Change the DBMS for the physical model.

    Menu > Database > Change Current DBMS

    From the drop down menu pick the option Microsoft SQL Server 2012 - 1.4.4.0 as shown in the figure below.

    Change DBMS
    Change DBMS

From now on this will be your default DBMS when you create a new physical model.

Step 7. Configure Settings Sets

When you create a physical model, PowerDesigner is capable of generating the proper Data Definition Language code, in short DDL. You can change the behaviour of the DDL generation. For example, for which object types to generate DDL and for which object types not to generate DDL.

We have provided default templates for these settings. These templates and their settings are important. This is because of our design choice to not implement all model object types in the database.

{info} Although this is out of scope for the installation guide an example will help in understanding the above mentioned design decision. In a technical staging model, you have the option to create a primary key on a table. This metadata information will be used in our code generation. However, when we implement a technical staging model, we do not want to create a unique primary key constraint in the database as this might result in loading errors when the table is populated. In the settings set configuration, this is exactly what we can do: ignore the creation of certain DDL statements.

  1. Open the menu.

    Menu > Database > Generate Database

    This will open the dialog as shown in the figure below.

    Configure PowerDesigner settings set dialog
    Configure PowerDesigner settings set dialog

  2. Click the file icon in the lower right of the dialog.

    This will open a file browser as you have seen earlier in this install guide.

    Select the directory I-REFACTORY-MODELLER-PATH\settings-sets.

Step 8. Validate the installation

  1. Shutdown your PowerDesigner application.

    You do not have to save anything so you can safely answer no when you are asked to save.

  2. Open the PowerDesigner application again.

  3. Create a new model

    We are going to create a new physical model based on the templates we have provided.

    Menu > File > New Model > Templates > Technical Staging model > OK

    {info} When a message "Could not find the management model, is it opened?" is shown click OK.

    When all sorts of errors are shown, keep in mind that PowerDesigner 16.5 uses Visual Basic Script. This is part of the .NET framework. You'll need .NET framework version 3.5 to work with this PowerDesigner version. You can find more information about .NET framework version 3.5 for Windows 10 here: Install Framework. Restart Windows, restart PD and these errors should be gone.

    A new physical model is created in PowerDesigner.

  4. Check settings

    Check the following settings:

    • Menu > Database > Change Current DBMS

      The value for current DBMS should be Microsoft SQL Server 2012 - 1.4.4.0

    • Menu > Database > Generate Database

      The value for settings set should be Generate technical staging

    • Object browser > Open Extensions folder

      A list of at least 6 extensions should be present, all beginning with i-refact

    • Menu > Tools > General Options > Named Paths

      The named paths, should be present (as created in Step 3. Change General Options - Create named paths)

Installation completed

If all the settings are ok, the installation is correct and you can start modelling.

To have an overview about how i-refactory modeller works, you can go to i-refactory modeller overview.

Constraint violation actions are applicable to certain constraint categories. Not all combinations of constraint categories and violation actions are allowed.

An attribute must have a value, whatever that value may be. It must not be NULL.

A data type of an attribute defines what value an attribute can hold. The data type specifies what type of mathematical, relational, or logical operations can be applied to it without causing an error.

An attribute datatype constraint is the most basic constraint type. It checks for the datatypes we support and have implemented.

For example, we check for string, length of string, integer, date, etc. In the following figure you can see the supported data types by PowerDesigner.

Image is omitted: Supported data types

Constraints can be violated and there are some actions that can be performed when a violation occurs. The possible actions are: EMPTY COLUMN, NO ACTION and SKIP ROW.

An attribute value constraint is an expression that is evaluated. The person who writes the expression is responsible for the correctness of it. The expression should be formulated in a positive way and lead to a Boolean answer. If the expression validates to True, than the value is correct.

Examples

  • The values in attribute X has to be bigger than 10: X > 10
  • The email address has to be in a certain pattern: email address LIKE '%_@_%.__%'

A Concept Integration Model is also a central facts model on which you place integration patterns. It is not required to create a concept integration model, but it can be very useful.

Every constraint is assigned to a constraint classification.

The main purposes of the Generic Data Access Layer (GDAL) are to provide logical perspectives for data consumption and to manage CRUD actions.

A generic data access model is a virtual data model that acts as an interface bridge between consumer applications and the central fact storage.

Every attribute is assigned to an attribute classification.

An entity record constraint checks whether an attribute meets the requirements set by another attribute belonging to the same entity.

The main purpose of the Logical Validation Layer (LVL) is to transform the data received from external data sources to fit into the logical data model structure. It is also responsible for validating deliveries. The Logical Validation Layer is also known as the Historical Staging In (HSTGIN) Layer.

The logical validation model is the representation of a single external data source in a logical format. It represent how data delivered by a specific tenant should be transformed, temporalized and validated in the {popup}logical validation layer. The logical validation model is also known as Historical Staging model (HSTGIN).

Multi-active attributes are attributes that contain a business key to provide multiple context records at the same time. For example: a customer has multiple types of phone numbers. “Home”, “Work” and “Mobile”. In that case we add a dependent entity on customer with key “Phone Nbr Type”. This is to prepare for the CFPL multi-active key on customer.

The main purpose of the Technical Staging Layer (TSL) is to create a common starting point for further data processing. It receives data delivered from external data sources and temporally stores them in a database. The input data should be in a tabular format (rows and columns).

Bi-temporal attribute is an attribute that changes over time: they follow a valid timeline. For example, a Part may have a price valid for December and a price valid for January.

Every entity is assigned to an entity classification and to a parent entity classification. The possible values for entity classification are: ALTERNATE KEY CONTEXT, ATTRIBUTE CONTEXT, GENERALIZATION,HELPER, REFERENCE CONTEXT, STABLE, STABLE DEPENDENT and STABLE INDEPENDENT

Entity Set Constraint An entity set constraint can be used to perform a check concerning values of two or more attributes that belong to different entities or to perform a check concerning the value of an attribute with respect to a set of values.

A Set Constraint Helper is a helper in the logical validation model. It is the implementation of a set constraint. The helper returns the records of an entity for a given set constraint, where the instances of this entity do not meet the definition of this set constraint.

The business requirements describe how data should be delivered for the data consumers (end users or applications) in terms of concepts, relationships between concepts and constraints to validate the data. These requirements can be described in a logical data model, for example.

A Business Rule Helper is a helper in the central facts model. It is a set-based calculation of derived facts. You need to use a Business Rule Helper if you want to make a calculation and want to keep a transaction history of the results of this calculation. You use the existing entities from the central facts model as input. The results of the helper must be materialized in 'regular' fact entities, such as Anchors and Contexts, to make them accessible in the Generic Data Access Layer.

Closed Open means that the timeline is valid from (vanaf in Dutch) the supplied valid start date until - but not including - (tot in Dutch) the supplied valid end date. In practice, this means that the start date of a valid time record is equal to the end date of the previous valid time record.

You need to create context-based entities when a set of data may be delivered within the boundaries of a parent context. A context-based entity applies when:

  • At least 2 entities are delivered.
  • A context relationship exists between these 2 entities. One entity is the parent context of the other entity.
  • The parent context entity is delivered as a delta and the child entity is delivered as a full set.

You need to create context-based entities when a set of data may be delivered within the boundaries of a parent context. A context-based entity applies when:

  • At least 2 entities are delivered.
  • A context relationship exists between these 2 entities. One entity is the parent context of the other entity.
  • The parent context entity is delivered as a delta and the child entity is delivered as a full set.

The Management Model contains the PowerDesigner objects for the Unified Anchor Modelling (UAM). When a UAM object is created, a so-called PowerDesigner replica of the corresponding Management Model object is created. This means that certain properties such as metadata columns and column stereotypes are configured in the Management Model and cannot be changed. The replication settings specify which elements of an object can be changed after creating a replica from the template object. It is possible to override the replication settings of an UAM object and change a specific property.

The temporal atomic type describes the datatype of the temporal attributes|

The main purposes of the Central Facts Layer (CFL) is to store data historically. It can also integrate data from different sources. The Central Facts Layer is also known as Central Facts Persistency Layer (CFPL)

The central facts persistence implementation model is the representation of facts in an anchorized data model with the ability to integrate multiple logical models.

In the context of i-refactory, data transformation refers to operations involved in turning raw data readily useful and closer to the business requirements.

Integration patterns are used to integrate entities from different data models. If two or more entities from different data models share the same business key, you can use the Integration Pattern named Key Root. It is a good practice to capture integration patterns in a separate model, named Concept Integration Model.

An attribute is mandatory when its value can not be empty (NULL).

A Physical Data Model (PDM) represents how data will be implemented in a specific database.

{note} The i-refactory uses four PDMs: technical staging model, logical validation model, central facts model and generic access model. Each one of these models is implemented as an additional database, which is used to store data from external and internal data sources.

Reverse engineering is the process of reconstructing a physical and/or Entity Relationship (ER) model from an existing data source. The purpose of reverse engineering is to avoid manual work as much as possible.

Architecture layer

The core of the i-refactory architecture has four layers: TSTGIN, LVL, CFL and GDAL. There are also two auxiliary layers: UCLVL and EXT.

If an entity has one or more attributes that changes over time and you want to keep track of when a attribute is valid at a certain transaction time, then you have a special case of a regular dependent entity, called bi-temporal entity. The bi-temporal entity stores historical data with two timelines. The primary key of the bi-temporal entity is composed by the primary key of the parent entity and the valid start date attribute. The attribute that changes over the valid time is called a bi-temporal attribute.

If an entity has one or more attributes that changes over time and you want to keep track of when a attribute is valid at a certain transaction time, then you have a special case of a regular dependent entity, called bi-temporal entity. The bi-temporal entity stores historical data with two timelines. The primary key of the bi-temporal entity is composed by the primary key of the parent entity and the valid start date attribute. The attribute that changes over the valid time is called a bi-temporal attribute.

A delivery agreement is a contract between a Tenant and a Logical Implementation Model or Generic Data Access model. An agreement has a duration. The delivery agreement set the architecture layer (interface) where the data should be ingested as well as the default settings to be applied to the deliveries.

A dependency mapping is a mapping between a helper (or BR helper) and a source entity used in the query of the helper. The helper and the source entity must belong to the same model.

  • Default dependency is set on entity level (source entity to helper entity)
  • To allow lineage on attribute level, via the Mapping editor, you could manually add the dependency on attribute level.

An Independent Entity is an entity that implements an Anchor for a Business Key that ‘stands alone’ e.g. that does not contain a reference to another Entity.

An Independent Entity is an entity that implements an Anchor for a Business Key that ‘stands alone’ e.g. that does not contain a reference to another Entity.

A Logical Data Model (LDM) matches the language, structure and quality of the business, regardless of the physical data implementation. The Logical Data Model reflects the business requirements.

A delivery may be considered as "untrusted" if deletes of data in the Logical Validation Layer have taken place and the processing of new deliveries cannot 100% rely (trust) on having enough statistics and data available to detect logical deletes, to determine the exact delta and to execute set based validations.

A delivery may be considered as "untrusted" if deletes of data in the Logical Validation Layer have taken place and the processing of new deliveries cannot 100% rely (trust) on having enough statistics and data available to detect logical deletes, to determine the exact delta and to execute set based validations.

A Dependent Entity is an entity that implements an Anchor for a Business Key that ‘depends’ in its existence on another Entity. A Dependent Entity contains Business Key fields of which at least one is a foreign key (FK).

A Dependent Entity is an entity that implements an Anchor for a Business Key that ‘depends’ in its existence on another Entity. A Dependent Entity contains Business Key fields of which at least one is a foreign key (FK).

The transaction time in i-refactory is different from what is commonly understood by transaction time. Transaction time is usually seen as the moment when a fact was stored in the database. In the i-refactory, the transaction time is the time, as dictated by the source system, not by the i-refactory database.

The Attribute type links the attribute to one of the existing interfaces.

Computed columns are columns whose content is computed from values in other columns in the table.

Functional date A functional date or time is a point in time and is defined by a user. An example is an order date or date of birth.

The technical model (also known as Technical Staging In model: TSTGIN) is a representation of how exactly one delivery from a specific data source will be processed in the technical staging layer.

Generalization is the process of extracting shared characteristics from two or more classes (hyponyms), and combining them into a generalized superclass (hypernym). For example: an 'employee' and a 'customer' are both 'persons'.

The Mapping Editor provides a graphical interface for creating and viewing mappings between models. It provides a global view of all the mappings related to the entities of a given model, allowing you to quickly identify those which are mapped and not mapped.

When a certain fact can change over time and you need to capture when that fact is valid in the real world, you can add a valid start date and a valid end date to the entity.

A valid time tells us in which period a record is valid. While a functional date represents just one point in time, the valid time has a begin and an end date, for example:

  • For Order item 123, a Retail price of 10.00 was valid from 2019-01-01 to 2019-06-01.
  • For Order item 123, a Retail price of 12.00 was valid from 2019-06-01 to 2020-01-01.

Alternate key is an attribute or a group of attributes whose values uniquely identify every record in an entity, but which is not the primary key

Candidate key

A candidate key consists of one or more attributes and meets the following requirements:

  • Unique: The value of the key defines uniquely one instance of a concepts. There are no double values.
  • Non-volatile: (Almost) doesn't change.
  • Minimal: Contains only the elements needed.

There are two kinds of candidate keys:

  • primary key
  • alternative key

Normalization is the process of decomposing tables in a database in order to reduce data redundancy and improve data integrity.

A strongly typed model is a model in which each all attributes have a predefined data type, for example: integers, doubles, date.

Surrogate Key A surrogate key is a system generated unique identifier that does not have any contextual or business meaning.

Business Key

A business key is an unique identifier that has business meaning and exists in the real world outside of the database. It consists of a column or a set of columns that already exists in a table. A business key is also known as a natural key

A Key Root Hub is an integration concept that must be used when the exact same business concept or independent business key occurs in different models. The Hubs for this independent business key in the different UAM models are all subtypes of the Keyroot Hub.

A relationship shows how two entities are related to one another. For example, a customer can place an order, and a order can have a customer.

Every Attribute has an atomic type (data type) which is linked to the attribute type of that attribute.

The cardinality shows how many instances of an entity can take place in a relationship.

The cardinality shows how many instances of an entity can take place in a relationship.

An enumeration consists of the list of values that a given attribute should adhere to.

{example} An order can have different statuses, such as shipped,packing,created anddone. Other statuses are not allowed.

Foreign Key

A foreign key is an attribute or a set of attributes that refers to the primary key of another entity. The original entity containing the primary key is called the 'parent' entity and the entity containing the foreign key is called the 'child' entity.

A natural key is an unique identifier that has business meaning and exists in the real world outside of the database. It consists of an column or a set of columns that already exists in a table. A natural key is also known as a business key

The primary key is an assigned key that consists of a minimal set of attributes to uniquely specify an instance of a record. The attribute or a combination of attributes should meet the following characteristics:

  • Unique: The attribute values of the key uniquely identify one instance of a concept. There are no duplicate instances.
  • Non-volatile: The key does not change.
  • Mandatory: All values are filled; there are no NULL values.

It is good practice to choose a primary key that also meet the following characteristic:

  • Safe: Doesn't contain private or sensitive information, such as a social security number.

Constraints are related to the other elements depending of the type of the constraint. Certain constraints are associated to attributes, entities, helper entities, unique keys or relationships between entities.

An attribute may be assigned to one or more entities (ex: acm_exists_ind) and an entity may have several attributes

Each layer may have one or more interfaces. The amount of interfaces depend on how many tenants and delivery agreements have been configured.

Namespace is what in the terminology of SQL Server is called database schema.|

A Delivery is a container that holds the specification of what is actually pushed to the i-refactory platform. This specification consists of a list of entities.

A Delivery is a container that holds the specification of what is actually pushed to the i-refactory platform. This specification consists of a list of entities.

Key Root A Key Root is a central repository for Business Keys. A Key Root ensures that similar records out of different data sources are identified by both the same Business Key as the Surrogated Key.

Context

A Context is a temporal table with a transaction start and end date. The Context tracks all changes of the context attributes related to a business key in the transaction time. This means that every change of an attribute value in a source system leads to a new record in the Context. The old record is end dated with the load date and the new record is start dated with the load date.

Hyponym is a term that denotes a subcategory of a more general class. For example: 'cat' and 'dog' are a hyponyms of 'animal'.

A mapping establishes relationships between concepts of separate data models. It creates a link between entities and attributes from a source model to related entities and attributes in the target model. A source model should precede the target model in the i-refactory architecture.

oasi_bk is an abbreviation for One Attribute Set Interface (OASI) with business keys. A normal view in the generic data access layer (GDAL) consists of the surrogate key, foreign key and attributes. The oasi_bk-view in the GDAL is a view where the business key(s) are also shown.

A subtype is a subgroup of an entity. You can create a subtype if a group of instances share some attributes and relationships that only exist for that group. For example, entity Customer can have a subtype Company and a subtype Person. They share the common attribute customer number, and can have some attributes of their own. Such as birth date for a Person. The entity Customer is called a supertype.

A subtype:

  • inherits all attributes of the supertype
  • inherits all relationships of the supertype
  • usually has one or more own attributes
  • can have subtypes of its own

Anchor: Independent Entity

An Independent Entity is an entity that implements an Anchor for a Business Key that ‘stands alone’ e.g. that does not contain a reference to another Entity.

Anchor: Dependent Entity

A Dependent Entity is an entity that implements an Anchor for a Business Key that ‘depends’ in its existence on another Entity.

A domain will help you to identify the types of information in your model. It defines the set of values for which a column is valid. A domain can specify a data type, length, precision, mandatoriness, check parameters, and business rules. It can be applied to multiple columns, which makes it easier to standardize data characteristics for columns in different tables.

Each interface may have one or more entities and one entity belongs to only one interface. An entity belongs to an i-refactory data model.

Each interface may have one or more entities and one entity belongs to only one interface. An entity belongs to an i-refactory data model.

A helper entity creates a derived entity and can be used when you need to transform, filter, or calculate data. The purpose of a helper differs per model:

  • Technical model: a helper is used to transform data.
  • Logical validation model: a helper is an implementation of a set constraint (Set Constraint Helper).
  • Central facts model: a helper is used for a set-based calculation of derived facts (Business Rule Helper).

HSTGIN is the abbreviation of Historical STaging IN. It is an older term to indicate the Logical Validation Model or Logical Validation Layer.

A schema is a set of database objects, such as tables, views, triggers, stored procedures, etc. In some databases a schema is called a namespace. A schema always belongs to one database. However, a database may have one or multiple schema's. A database administrator (DBA) can set different user permissions for each schema.

Each database represents tables internally as <schema_name>.<table_name>, for example tpc_h.customer. A schema helps to distinguish between tables belonging to different data sources. For example, two tables in two schema's can share the same name: tpc_h.customer and complaints.customer.

A Tenant is a delivering party for a dataset or datarecord as agreed in the Delivery Agreement.

TSTGIN is the abbreviation of Technical STaging IN. It is an older term to indicate the Technical Model or Technical Staging Layer.

An index organizes data in a way that improves the speed of data retrieval from a database. To maintain the index data structure, there is a cost of additional writes and storage space.

An index organizes data in a way that improves the speed of data retrieval from a database. To maintain the index data structure, there is a cost of additional writes and storage space.

The acronym CRUD stands for create, read, update, and delete. These are the four basic functions of persistent storage.

OLAP is a acronym for Online Analytical Processing. OLAP is category of software tools which provide analysis of data for business decisions. It uses complex queries to analyze aggregated historical data from OLTP systems.The primary objective is data analysis and not data processing.

OLTP is a acronym for Online transaction processing. OLTP captures, stores, and processes data from transactions in real time. Its primary objective is data processing and not data analysis.

A hub or independent entity is an entity that implements an Anchor for a business key that ‘stands alone’ e.g. that does not contain a reference to another entity. An independent entity contains business key fields, that show up as alternate key (AK), and the primary key (PK) is its surrogate key (ID).

A key is a combination of one or more attributes of an entity that uniquely defines one instance of that entity.