<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/xhtml;charset=UTF-8"/>
<title>Frepple / Buffer </title>
<link rel='stylesheet' href='../styles.css' type='text/css' />
<!--PageHeaderFmt-->
</head>
<body>
<div id="container">
<div id="menubar">
<div id="logo" align="center">
<br/><img src='../frepple.bmp' alt="frepple" /><br/>
<a href='http://www.frepple.com/'>
<strong>a Free<br/>Production Planning<br/>Library</strong>
</a></div>
<div id="menu">
<br/>
<h3><a href='../Main/HomePage.html'>Main</a></h3>
<h3><a href='../UI/Main.html'>User Manual</a></h3>
<h3><a href='../Tutorial/Main.html'>Tutorial</a></h3>
<h3><a href='Main.html'>Reference Manual</a></h3>
<h3><a href='../Main/FAQ.html'>FAQ</a></h3>
<h3><a href='../reference/index.html'>C++ API</a></h3>
<br/><div>
</div>
</div>
</div>
<div id="content">
<br/>
<!--PageText-->
<div id='wikitext'>
<p><a class='wikilink' href='../Main/HomePage.html'>Main</a> > <span class='wikitrail'><a class='wikilink' href='Main.html'>Reference Manual</a> > <a class='wikilink' href='Modeling.html'>Modeling</a> > <a class='selflink' href='ModelingBuffer.html'>Buffer</a></span>
</p>
<p class='vspace'>A buffer is a storage for a item.<br />It represents a place where inventory of an item is kept.
</p>
<p class='vspace'>Different types of buffers exist:
</p><ul><li><a href='ModelingBuffer.html#buffer_default'>buffer_default</a>:<br /> The default buffer uses an "producing" operation to replenish it with additional material.
</li><li><a href='ModelingBuffer.html#buffer_procure'>buffer_procure</a>:<br /> A buffer that is replenished by a supplier. A number of parameters control the re-ordering policy: classic re-order point, fixed time ordering, fixed quantity ordering, etc...
</li><li><a href='ModelingBuffer.html#buffer_infinite'>buffer_infinite</a>:<br /> An infinite buffer has an infinite supply of the material is available.
</li></ul><div class='vspace'></div><h2>Fields</h2>
<table border='1' width='100%' ><tr><td width='20%' valign='top'><strong>Field</strong>
</td><td width='20%' valign='top'><strong>Type</strong>
</td><td width='60%' valign='top'><strong>Description</strong>
</td></tr><tr><td valign='top'>name
</td><td valign='top'>non-empty string
</td><td valign='top'>
<p>Name of the buffer.<br />This is the key field and a required attribute.
</p></td></tr><tr><td valign='top'>description
</td><td valign='top'>string
</td><td valign='top'>
<p>Free format description.
</p></td></tr><tr><td valign='top'>category
</td><td valign='top'>normalizedString
</td><td valign='top'>
<p>Free format category.
</p></td></tr><tr><td valign='top'>subcategory
</td><td valign='top'>normalizedString
</td><td valign='top'>
<p>Free format subcategory.
</p></td></tr><tr><td valign='top'>owner
</td><td valign='top'>buffer
</td><td valign='top'>
<p>Buffers can be organized in a hierarchical tree.<br />This field defines the parent buffer.<br />No specific planning behavior are currently linked to such a hierarchy.
</p></td></tr><tr><td valign='top'>members
</td><td valign='top'>list of buffer
</td><td valign='top'>
<p>Buffers can be organized in a hierarchical tree.<br />This field defines a list of child buffers.
</p></td></tr><tr><td valign='top'>location
</td><td valign='top'>location
</td><td valign='top'>
<p>Location of the buffer.<br />Default is null.<br />The working hours and holidays for the buffer are taken from the 'available' calendar of the location.
</p></td></tr><tr><td valign='top'>item
</td><td valign='top'>item
</td><td valign='top'>
<p>Item being stored in the buffer.<br />Default is null.
</p></td></tr><tr><td valign='top'>onhand
</td><td valign='top'>double
</td><td valign='top'>
<p>Inventory level at the start of the time horizon.<br />Default is 0.
</p></td></tr><tr><td valign='top'>carrying_cost
</td><td valign='top'>double
</td><td valign='top'>
<p>The cost of carrying inventory in this buffer.<br />The value is an annual percentage of the item sales price.<br />The default value is 0.0.
</p></td></tr><tr><td valign='top'>minimum
</td><td valign='top'>calendar
</td><td valign='top'>
<p>Refers to a calendar storing the desired minimum inventory level, aka safety stock.<br />The solver treats this as a soft constraint, ie it tries to meet this inventory level but will go below the minimum level if required to meet the demand.<br />A problem is reported when the inventory drops below this level.
</p>
<p class='vspace'>The safety stock target is expressed as a quantity. If you want to define a safety stock target as a time value (aka days of inventory), you can set a post-operation time on the producing operation of the buffer.
</p></td></tr><tr><td valign='top'>maximum
</td><td valign='top'>calendar
</td><td valign='top'>
<p>Refers to a calendar storing the maximum inventory level.<br />This field is not used by the solver.<br />A problem is reported when the inventory level is higher than this limit.
</p></td></tr><tr><td valign='top'>producing
</td><td valign='top'>operation
</td><td valign='top'>
<p>This operation will be instantiated by the solver to replenish the buffer with additional material.
</p></td></tr><tr><td valign='top'>detectproblems
</td><td valign='top'>boolean
</td><td valign='top'>
<p>Set this field to false to supress problem detection on this buffer.<br />Default is true.
</p></td></tr><tr><td valign='top'>flows
</td><td valign='top'>list of flow
</td><td valign='top'>
<p>Defines material flows consuming from or producing into this buffer.
</p></td></tr><tr><td valign='top'>flowplans
</td><td valign='top'>list of flowplan
</td><td valign='top'>
<p>This field is populated during an export with the plan results for this buffer. It shows the complete inventory profile.<br />The field is export-only.<br />The description of the <a class='wikilink' href='ModelingOperationPlan.html#FLOW_PLAN'>flowplan model</a> is included in the section on operationplan.
</p></td></tr><tr><td valign='top'>level
</td><td valign='top'>integer
</td><td valign='top'>
<p>Indication of how upstream/downstream this entity is situated in the supply chain.<br />Lower numbers indicate the entity is close to the end item, while a high number will be shown for components nested deep in a bill of material.<br />The field is export-only.
</p></td></tr><tr><td valign='top'>cluster
</td><td valign='top'>integer
</td><td valign='top'>
<p>The network of entities can be partitioned in completely independent parts. This field gives the index for the partition this entity belongs to.<br />The field is export-only.
</p></td></tr><tr><td valign='top'>hidden
</td><td valign='top'>boolean
</td><td valign='top'>
<p>Marks entities that are considered hidden and are normally not shown to the end user.
</p></td></tr><tr><td valign='top'>action
</td><td valign='top'>
<p>A<br />C<br />AC (default)<br />R
</p></td><td valign='top'>
<p>Type of action to be executed:
</p><ul><li>A: Add an new entity, and report an error if the entity already exists.
</li><li>C: Change an existing entity, and report an error if the entity doesn't exist yet.
</li><li>AC: Change an entity or create a new one if it doesn't exist yet.
</li><li>R: Remove an entity, and report an error if the entity doesn't exist.
</li></ul></td></tr></table>
<p class='vspace'><a name='buffer_default' id='buffer_default'></a>
</p><h2>buffer_default</h2>
<p>The default buffer uses an "producing" operation to replenish it.
</p>
<p class='vspace'>No fields are defined in addition to the ones listed above.
</p>
<p class='vspace'><a name='buffer_procure' id='buffer_procure'></a>
</p><h2>buffer_procure</h2>
<p>A procurement buffer is replenished by a supplier.
</p>
<p class='vspace'>A number of parameters control the re-ordering policy: classic re-order point, fixed time ordering, fixed quantity ordering, etc...<br />The parameters LEADTIME, MININVENTORY and MAXINVENTORY define a replenishment with a classical re-orderpoint policy. The inventory profile will show the typical sawtooth shape.<br />The parameters MININTERVAL and MAXINTERVAL put limits on the frequency of replenishments. The inventory profile will have "teeth" of variable size but with a controlled interval.<br />The parameters SIZE_MINIMUM, SIZE_MAXIMUM and SIZE_MULTIPLE put limits on the size of the replenishments. The inventory profile will have "teeth" of controlled size but with variable intervals.<br />Playing with these parameters allows flexible and smart procurement policies to be modelled.
</p>
<p class='vspace'>Note that frePPLe doesn't include any logic to set these parameters in an optimal way. The parameters are to be generated externally and frePPLe only executes based on the parameter settings.<br />At a later stage a module to compute these parameters could be added.
</p>
<p class='vspace'>The PRODUCING field is unused for this buffer type. <br />Propagation through a bill of material will be stopped at a procurement buffer.
</p>
<div class='vspace'></div>
<table border='1' width='100%' ><tr><td width='20%' valign='top'><strong>Field</strong>
</td><td width='20%' valign='top'><strong>Type</strong>
</td><td width='60%' valign='top'><strong>Description</strong>
</td></tr><tr><td valign='top'>leadtime
</td><td valign='top'>duration
</td><td valign='top'>
<p>Time taken between placing the purchase order with the supplier and the delivery of the material.<br />When the "LEADTIME" constraint is enabled in the solver, it won't create any new procurement orders that would need to start in the past.
</p></td></tr><tr><td valign='top'>fence
</td><td valign='top'>duration
</td><td valign='top'>
<p>Time window (from the current date of the plan) during which procurement orders are expected to be released.<br />When the "FENCE" constraint is enabled in the solver, it won't create any new operation plans in this time fence. Only the externally supplied existing procurement plans will then exist in this time window.
</p></td></tr><tr><td valign='top'>mininventory
</td><td valign='top'>Positive double
</td><td valign='top'>
<p>Inventory level triggering a new replenishment.<br />The actual inventory can drop below this value.
</p></td></tr><tr><td valign='top'>maxinventory
</td><td valign='top'>Positive double
</td><td valign='top'>
<p>Inventory level to which we try to replenish.<br />The actual inventory can exceed this value.
</p></td></tr><tr><td valign='top'>mininterval
</td><td valign='top'>duration
</td><td valign='top'>
<p>Minimum time between replenishments.<br />The order quantity will be increased such that it covers at least the demand in the minimum interval period. The actual inventory can exceed the target set by the MinimumInventory parameter.
</p></td></tr><tr><td valign='top'>maxinterval
</td><td valign='top'>duration
</td><td valign='top'>
<p>Maximum time between replenishments.<br />The order quantity will replenish to an inventory value less than the maximum when this maximum interval is reached.
</p></td></tr><tr><td valign='top'>size_minimum
</td><td valign='top'>Positive double
</td><td valign='top'>
<p>Minimum quantity for a replenishment.<br />This parameter can cause the actual inventory to exceed the target set by the MinimumInventory parameter.
</p></td></tr><tr><td valign='top'>size_maximum
</td><td valign='top'>Positive double
</td><td valign='top'>
<p>Maximum quantity for a replenishment.<br />This parameter can cause the maximum inventory target never to be reached.
</p></td></tr><tr><td valign='top'>size_multiple
</td><td valign='top'>Positive double
</td><td valign='top'>
<p>All replenishments are rounded up to a multiple of this value.
</p></td></tr></table>
<p class='vspace'><a name='buffer_infinite' id='buffer_infinite'></a>
</p><h2>buffer_infinite</h2>
<p>An infinite buffer has an infinite supply of the material is available.
</p>
<p class='vspace'>The PRODUCING field is unused for this buffer type. <br />Propagation through a bill of material will be stopped at an infinite buffer.
</p>
<div class='vspace'></div><h2>Example XML structures</h2>
<ul><li>Adding or changing a buffer
</li></ul><pre> <plan>
<buffers>
<buffer name="item a @ location b">
<item name="item a" />
<location name="location b" />
<onhand>10</onhand>
</buffer>
</buffers>
</plan>
</pre><div class='vspace'></div><ul><li>Update the current inventory information of an existing buffer
</li></ul><pre> <plan>
<buffers>
<buffer name="item a @ location b" onhand="100" action="C" />
</buffers>
</plan>
</pre><div class='vspace'></div><ul><li>Deleting a buffer
</li></ul><pre> <plan>
<buffers>
<buffer name="item a @ location b" action="R"/>
</buffers>
</plan>
</pre><div class='vspace'></div><h2>Example Python code</h2>
<ul><li>Adding or changing a buffer
</li></ul><pre> it = frepple.item(name="item a")
loc = frepple.location(name="location b")
buf = frepple.buffer(name="item a @ location b",
onhand=10, item=it, location=loc)
</pre><div class='vspace'></div><ul><li>Update the current inventory information of an existing buffer
</li></ul><pre> buf = frepple.buffer(name="item a @ location b",
onhand=10, action="C")
</pre><div class='vspace'></div><ul><li>Deleting a buffer
</li></ul><pre> buf = frepple.buffer(name="item a @ location b", action="R")
</pre><div class='vspace'></div><ul><li>Iterate over buffers, flows and flowplans
</li></ul><pre> for b in frepple.buffers():
print "Buffer:", b.name, b.description, b.category
for l in b.flows:
print " Flow:", l.operation.name, l.quantity,
l.effective_start, l.effective_end
for l in b.flowplans:
print " Flowplan:", l.operationplan.operation.name,
l.quantity, l.date
</pre>
</div>
<!--PageFooterFmt-->
<!--HTMLFooter-->
</div></div>
</body>
</html>
