Each table is recreated as an object called an Entity class. Each column of the table becomes a property of the Entity class called a DataField. You can add properties for calculated fields too. This becomes the framework where you add business logic associated with columns and the table itself.

An Attribute allows the programmer to annotate a class or property with "metadata". Within BLD, Attributes describe your business rules and annotate the properties of your Entity classes. These are called DataAnnotation Attributes.

Microsoft's DataAnnotation Attribute classes from the System.ComponentModel.DataAnnotations namespace get you started.

BLD introduces improved versions of most of those Attributes and covers many new business logic cases within its own PeterBlum.DES.DataAnnotations namespace.

public class Product
{
   [DESDA.CharacterSet(LettersLowercase=true, LettersUppercase=true, Digits=true,  
      Space=true, DiacriticLetters=true, OtherCharacters="'",
      ErrorMessage="Illegal character", 
      SummaryErrorMessage="{LABEL} has an illegal character.")]
   [DESDA.DisplayName("Product name", ShortDisplayName="Name")]
   public string ProductName { get; set; }

   [DESDA.CurrencyDataType(AllowNegatives=false, UseCurrencySymbol=true, MaxWholeDigits=4)]
   [DESDA.Description("The price of one unit")]
   [DESDA.DisplayName("Unit Price")]
   public System.Nullable<decimal> UnitPrice { get; set; }

   [DESDA.CurrencyDataType()]
   [DESDA.DisplayName("Value of Stock")]
   [DESDA.CalculationDescriptor("if (Not Discontinued) then {UnitPrice * UnitsInStock} else novalue")]
   [DESDA.ColumnRestriction("Customer", DESDA.DenyAccess.All)]
   [DESDA.SortableColumn(SortExpression="UnitPrice * UnitsInStock", Sortable=true)]
   public decimal ValueOfStock
   {
      get
      { 
         if (!Discontinued)
            if (UnitPrice.HasValue && UnitsInStock.HasValue)
               return UnitPrice.Value * UnitsInStock.Value;
         return 0.0M;
      }
   }
}

Each property's type (like Integer, String, and DateTime) are usually too broad to describe the actual data of the column. A string can represent numerous types, such as HTML, a phone number, or a name. Your business logic needs to identify the specific type because there are rules specific to them. For example, a phone number is a pattern that needs to be checked against a regular expression pattern and that pattern may differ based on the address location.

The System.ComponentModel.DataAnnotations.DataTypeAttribute helps, although it provides a relatively short list of data types. BLD includes numerous DataType Attribute classes, many with a variety of properties to customize the business rules. You can also create your own DataType attributes.

[DESDA.CurrencyDataType(AllowNegatives=false, UseCurrencySymbol=true, MaxWholeDigits=4)]
public System.Nullable<decimal> UnitPrice { get; set; }

[DESDA.DateDataType(ErrorMessage="This is an error",
   SummaryErrorMessage="The {LABEL1} is an illegal date.", DisplayOrder=0)]
public DateTime BirthDate { get; set; }

[DESDA.EnumeratedAttribute(EnumeratedType=typeof(MyNamespace.OutputMode)]
public int OutputMode { get; set; }

[DESDA.EnumeratedString("Mr.|Dr.|Mrs.|Hon.")]
public string TitleOfCourtesy { get; set; }

Validation is perhaps the first type of business rule you think of. The System.ComponentModel.DataAnnotations namespace provides you with several rules, but this hardly covers the real world cases you will face. BLD improves upon the originals and is designed for expansion when you have additional cases.

Here are a few improvements made with BLD's Validator Attributes:

• Interacts with a factory that creates different Validator classes based on the user interface (or lack thereof). That factory is prepopulated to support ASP.NET Web Forms (using DES Validation framework validators) and UI neutral validation. You could create validators for MVC, Silverlight, etc. that are delivered by the factory.
• Covers cases that involve multiple columns, such as comparing the value of column A to column B.
• Due to the richness of DES Validation Framework validators, these attributes are also rich with properties to customize the rules.
• When combined with the DependencyAttributes (below), validation rules can be enabled based on the values of other columns. The DES Validation Framework uses the term "Enabler" to describe this capability.
• Their error message strings employ tokens that get substituted with live data and the actual field labels shown in the Web Form. This reduces the need to create error messages within the UI layer.

[DESDA.Required(DisplayOrder=1)] 
[DESDA.Range("1900-01-01", "1999-12-31", DisplayOrder=5)]
[DESDA.DateDataType(ErrorMessage="This is an error", 
   SummaryErrorMessage="The {LABEL} is an illegal date.", DisplayOrder=0)]
[DESDA.CompareTwoColumns("HireDate", PeterBlum.DESDA.ConditionOperator.LessThan, 
   DisplayOrder=10)]
public object BirthDate { get; set; }

[DESDA.DateDataType(ErrorMessage="This is an error", 
   SummaryErrorMessage="The {LABEL} is an illegal date.")]
public object HireDate { get; set; }